Characteristics of Participants: Mean age for deployed veterans who were examined was 38.9 yrs. compared with 40.7 yrs. for non-deployed veterans who were examined (p<.0001). Mean income was $46,800 for deployed and $52,000 for non-deployed participants (p=.003). Non-deployed participants were more likely to be white (81.0% vs. 76.4%, p=.03), to be married (72.3% vs. 67.4%, p=.02), and to continue education past high school (42% vs. 32.5%, p<.0001). Results for Veterans: Both the physical and mental component scores derived from the SF-36 were significantly lower among deployed veterans who were examined. For the physical component score, the mean for the deployed group was 48.2 (s.d. 9.8) compared with 50.8 (s.d. 8.3) for the non-deployed group, p<.0001. The mental component score averaged 49.6 (s.d. 10.2) for the deployed group and 53.7 (s.d. 7.9) for the non-deployed group, p<.0001. There was a weak trend for a higher prevalence of fibromyalgia in the deployed group (3.1%) than in the non-deployed group (1.9%), [odds ratio 1.64, 95% confidence interval (.94, 2.87), p=.09]. There was a higher prevalence of chronic fatigue syndrome among deployed (1.6%) than non-deployed (0.4%), [odds ratio 4.58, 95% confidence interval (1.53, 13.64), p=.003]. Among the seven cognitive dysfunction factors, there was a trend towards a higher prevalence of impaired attention/working memory among deployed (6.6%) than non-deployed (4.2%), [odds ratio 1.60, 95% confidence interval (1.10, 2.35), p=.02]. PTSD after the Gulf War was more prevalent among deployed (10.1%) than non-deployed participants (3.2%), [odds ratio 3.41, 95% confidence interval (2.30, 5.05), p<.0001]. No differences were found for peripheral neuropathy and 6 of the 7 factors defined to assess cognitive dysfunction. Among secondary outcome measures, several categories of skin conditions were found to be more prevalent among deployed veterans. Results for Spouses: The mean score for the mental component scale was lower in the spouses of deployed participants (50.3 (s.d. 9.9)) than in the spouses of non-deployed participants (52.6 (s.d. 8.6), p<.0001). No other outcome measures for spouses were found to be related to deployment status of the veteran. Birth Defects: No statistically significant relationship between deployment status and prevalence of birth defects among first live born offspring born after the Gulf War was found. Summary: Although participation rates were lower than anticipated, we found little evidence of participation bias. Veterans deployed to the Gulf War have higher rates of chronic fatigue syndrome and post-Gulf War onset PTSD, and poorer health-related quality of life. Attention/working memory deficits and fibromyalgia may also be related to deployment to the Gulf War. Additional Comments: Additional analytic work remains: (a) the results have not been adjusted for covariates such as age, (b) certain subgroups were oversampled and the results are not adjusted for the study's original sampling methodology, (c) analysis of subgroups that are purported to be at increased risk of health impacts due to their type of service in the Gulf War has not been done.