['Medline, Embase, Cochrane Central Register of Controlled Trials, Dissertation Abstracts, SIGLE, the WorldWideWeb (Google) and the Community of Science Database were searched for relevant trials and references. Reference lists from relevant articles were scanned and the authors contacted to identify trials and obtain additional information. There were no language restrictions. Trials pre-1966 were not searched.', 'Studies were included if they were randomised controlled trials of conscious sedation comparing two or more drugs/techniques/placebo undertaken by the dentist or one of the dental team in children up to 16 years of age.', 'Reference lists from relevant articles were scanned and the authors contacted to identify trials and obtain additional information. There were no language restrictions. Trials pre-1966 were not searched.', 'Thirty-six studies (2810 participants) were included. The majority of the trials (30) were of high risk of bias, the other six trials were at unclear risk of bias. Twenty-eight different sedatives were used with or without inhalational nitrous oxide, and the dosages, mode and timing of administration varied greatly. The trials were grouped into placebo-controlled, dosage and head-to-head comparisons. Meta-analysis was possible for studies investigating oral midazolam vs placebo only. There is weak evidence from five trials at high risk of bias, that the use of oral midazolam in doses between 0.25 mg/kg to 0.75 mg/kg is associated with more co-operative behaviour compared to placebo; standardised mean difference (SMD) favoured midazolam (SMD 2.98, 95% CI 1.58 to 4.37, P < 0.001, I² = 91%). There was also very weak evidence from two trials which could not be pooled that inhalational nitrous oxide is more effective than placebo.'] Is weak evidence that oral midazolam an effective sedative agent for children undergoing dental treatment?