Abstract: This review includes seven trials with low to moderate risk of bias: five undertaken in children (987 participants) and two in adults (156 participants). An eighth trial in adults (40 participants) was at high risk of bias and did not provide any data for analysis. Good information about the effectiveness of adeno-/tonsillectomy is only available for the first year following surgery in children and for a shorter period (five to six months) in adults. We combined data from five trials in children; these trials included children who were 'severely affected' (based on the specific 'Paradise' criteria) and less severely affected. Children who had an adeno-/tonsillectomy had an average of three episodes of sore throats (of any severity) in the first postoperative year, compared to 3.6 episodes in the control group; a difference of 0.6 episodes (95% confidence interval (CI) -1 to -0.1; moderate quality evidence). One of the three episodes in the surgical group was the 'predictable' one that occurred in the immediate postoperative period. When we analysed only episodes of moderate/severe sore throat, children who had been more severely affected and had adeno-/tonsillectomy had on average 1.1 episodes of sore throat in the first postoperative year, compared with 1.2 episodes in the control group (low quality evidence). This is not a significant difference but one episode in the surgical group was that occurring immediately after surgery. Less severely affected children had more episodes of moderate/severe sore throat after surgery (1.2 episodes) than in the control group (0.4 episodes: difference 0.8, 95% CI 0.7 to 0.9), but again one episode was the predictable postoperative episode (moderate quality evidence). Data on the number of sore throat days is only available for moderately affected children and is consistent with the data on episodes. In the first year after surgery children undergoing surgery had an average of 18 days of sore throat (of which some - between five and seven on average - will be in the immediate postoperative period), compared with 23 days in the control group (difference 5.1 days, 95% CI 2.2 to 8.1; moderate quality evidence). When we pooled the data from two studies in adults (156 participants), there were 3.6 fewer episodes (95% CI 7.9 fewer to 0.70 more; low quality evidence) in the group receiving surgery within six months post-surgery. However, statistical heterogeneity was significant. The pooled mean difference for number of days with sore throat in a follow-up period of about six months was 10.6 days fewer in favour of the group receiving surgery (95% CI 5.8 fewer to 15.8 fewer; low quality evidence). However, there was also significant statistical heterogeneity in this analysis and the number of days with postoperative pain (which appeared to be on average 13 to 17 days in the two trials) was not included. Given the short duration of follow-up and the differences between studies, we considered the evidence for adults to be of low quality. Two studies in children reported that there was "no statistically significant difference" in quality of life outcomes, but the data could not be pooled. One study reported no difference in analgesics consumption. We found no evidence for prescription of antibiotics. Limited data are available from the included studies to quantify the important risks of primary and secondary haemorrhage. Adeno-/tonsillectomy leads to a reduction in the number of episodes of sore throat and days with sore throat in children in the first year after surgery compared to (initial) non-surgical treatment. Children who were more severely affected were more likely to benefit as they had a small reduction in moderate/severe sore throat episodes. The size of the effect is very modest, but there may be a benefit to knowing the precise timing of one episode of pain lasting several days - it occurs immediately after surgery as a direct consequence of the procedure. It is clear that some children get better without any surgery, and that whilst removing the tonsils will always prevent 'tonsillitis', the impact of the procedure on 'sore throats' due to pharyngitis is much less predictable. Insufficient information is available on the effectiveness of adeno-/tonsillectomy versus non-surgical treatment in adults to draw a firm conclusion. The impact of surgery, as demonstrated in the included studies, is modest. Many participants in the non-surgical group improve spontaneously (although some people randomised to this group do in fact undergo surgery). The potential 'benefit' of surgery must be weighed against the risks of the procedure as adeno-/tonsillectomy is associated with a small but significant degree of morbidity in the form of primary and secondary haemorrhage and, even with good analgesia, is particularly uncomfortable for adults.

Plain-language summary: This review included evidence available up to 30 June 2014. Seven trials with low to moderate risk of bias were included: five in children (987 participants) and two in adults (156 participants). An eighth trial in 40 adults was at high risk of bias and did not provide any data for analysis. Although some studies in children followed participants for two or three years, reliable information is only available for up to about one year after surgery due to the high number of participants missing follow-up after the first year. Some studies had recruited children who were more severely affected by tonsillitis than other studies (for example, they had tonsillitis more often and with more severe symptoms). Therefore, we grouped the children into 'severely affected' and 'less severely affected' subgroups. Two studies in adults had a short duration of follow-up (five to six months following surgery). We found that in general children affected by recurrent acute tonsillitis may have a small benefit from adeno-/tonsillectomy: this procedure will avoid 0.6 episodes of any type of sore throat in the first year after surgery compared to non-surgical treatment. The children who had surgery had three episodes of sore throat on average compared to 3.6 episodes experienced by the other children. One of the three episodes is the episode of pain caused by surgery. When it comes to avoiding bad sore throats, children who have more severe or frequent tonsillitis may benefit more from surgery compared to less severely affected children. In less severely affected children the potential benefits of adeno-/tonsillectomy are more uncertain. There are no good quality data for the effects of surgery in the second or later years after surgery. We did not find enough evidence to draw firm conclusions on the effectiveness of tonsillectomy in adults with chronic/recurrent acute tonsillitis. Evidence is only available for the short term and is of low quality. The data are also difficult to interpret as the studies do not take into account the days of pain that always follow the operation. Based on the two small trials, tonsillectomy seems to result in fewer days of sore throat in the first six months after surgery. Two of the studies in children said that they could not find a difference in quality of life outcomes and one study could not find a difference in the amount of painkiller that children took to help with their sore throats. Bleeding immediately after tonsillectomy or in the two weeks following surgery is an important complication. The studies did not provide good information to allow us to assess accurately the risk of these complications. We judged the quality of the evidence to be moderate for the data on children (this means that further research is likely to have an important impact on how confident we are in the results and may change those results). Quality is affected by a large number of children who are 'lost to follow-up' after the first year of the study. In addition, some children who are assigned to the 'no surgery' group end up having surgery. The quality of evidence for tonsillectomy in adults in adults is low. As always, any potential benefits of surgery should be carefully weighed against the possible harms as the procedure is associated with a small but significant degree of morbidity in the form of bleeding (either during or after the surgery). In addition, even with good pain relief medication, the surgery is particularly uncomfortable for adults.