BMC Public Health 2004, 4:27 http://www.biomedcentral.com/1471-2458/4/27 analysis if they had more than one symptom in the same category. Statistical analysis All analyses were performed using Stata 7.0 statistical soft- ware [16]. All p-values quoted are two-sided and values less than 0.05 were taken to indicate statistical signifi- cance. t-tests were conducted on log transformed data to compare the average number of ill health categories reported per subject in different groups. The association between deployment and ill health was explored using logistic regression analysis, calculating odds ratios and 95%CIs (with NGWV as baseline) for each ill health cate- gory. We adjusted for age at survey, service, rank, serving status at time of survey, smoking status and current alco- hol consumption in all models. Results Response Data supplied by all male respondents are analysed here (24,379 GWV; 18,439 NGWV). Characteristics of these men and of those reporting one or more medical prob- lems arising since 1990 are presented in Table 1. GWV responders were slightly younger than NGWV responders, and were more likely to have served in the Army, to not be an officer, to have left the Armed Services, to have ever smoked, and to have consumed larger amounts of alco- hol. However, the differences in the distributions were not large. Among those reporting one or more medical symp- tom/disease, GWV were again younger, more likely to serve in the Army, to not be an Officer, and to have ever smoked. Symptoms/diseases 61% of GWV reported at least one new medical symptom since 1990 compared with 37% of NGWV (adjusted OR 2.7, 95% CI 2.5–2.8). The data are presented by ill health category in Table 2 in order of frequency of reporting by GWV (highest to lowest). The most common symptoms/ diseases reported by GWV were skeletal and other muscu- lar symptoms (15.1%), 'other' symptoms (13.1%), gen- eral fatigue (10.8%), memory loss/lack of concentration (7.9%) and skin allergies (7.6%). Accidental injury (2.6%) was among one of the most common ill health categories reported by NGWV. Overall, GWV reported sig- nificantly more symptoms/diseases than NGWV. Among all those reporting one or more new symptom/disease since 1990, GWV reported a median of two different ill health categories per subject (range 1–23), while NGWV reported a median of one (range 1–17) (p < 0.001). For over 85% of categories of ill health, symptom/disease prevalence was higher among GWV (Figure 1; Table 2). Strongest associations with Gulf war service included mood swings (OR 20.9, 95%CI 16.2–27.0), memory loss/ lack of concentration (OR 19.6, 95% CI 15.5–24.8), night sweats (OR 9.9, 95% CI 6.5–15.2), general fatigue (OR 9.6, 95% CI 8.3–11.1) and sexual dysfunction (OR 4.6, 95%CI 3.2–6.6). Adjustment for potential confounding factors had little impact on these associations, none changing the ORs by more than about 3–4% on average. Gulf War syndrome (GWS) among GWV 23,103 GWV answered the question "Do you consider that you have "Gulf War Syndrome"?". 5.6% believed that they had the syndrome (GWS) and 40.9% stated that they were 'unsure' (Table 1). Among all GWV reporting one or more new symptom/disease since 1990, veterans who believed that they had GWS reported the highest number of different symptoms/diseases (median = 3; range 1–23), with those who were unsure (unsure-GWS) reporting more symptoms/diseases (median = 2; range 1–15) than those who stated that they did not (non-GWS) (median = 1; range 1–10 categories per subject); (χ2trend: p < 0.001). For all but one ill health category (accidental injury), those who believed that they had GWS reported the high- est symptom/disease prevalence, with unsure-GWS reporting intermediate frequencies for all categories (Table 3; Figure 2). Discussion This is the largest study of male UK veterans of the first Gulf war and the only one to approach all those deployed. Unlike other Gulf war studies, information on ill health arising since the war was collected using free text. Our study confirmed that GWV were significantly more likely to report at least one new medical problem since 1990 than a non-deployed comparison group. It also confirmed that veterans were more likely to report higher numbers of symptoms/diseases. These typically included skeletal and other muscular symptoms, general fatigue, memory loss/ lack of concentration, skin allergies, mood swings/aggres- sion and headaches. This pattern of symptom reporting is similar to that found in other studies of UK GWV [1-3], which looked at the same populations using different methods. For example, Unwin et al [1] found that GWV reported all symptoms (in pre-defined categories) at higher frequencies than NGWV in their study of a sample of UK veterans with two matched comparison groups, while we found that GWV reported higher prevalence in 85% of ill health categories. In terms of the nature of self-reported ill health, we found similar results to the range of symptoms that have been reported elsewhere. Gray et al's [17] study of GWV found that over 50 percent of diagnoses could be classified into four large categories: diseases of the musculoskeletal sys- tem and connective tissue (19.0%), mental disorders (14.7%), diseases of the respiratory system (10.5%) and diseases of the skin and subcutaneous tissue (9.4%). In Page 3 of 10 (page number not for citation purposes)