To assess the prevalence of self-reported symptoms and illnesses among military personnel deployed during the Persian Gulf War (PGW) and to compare the prevalence of these conditions with the prevalence among military personnel on active duty at the same time, but not deployed to the Persian Gulf (non-PGW). Cross-sectional telephone interview survey of PGW and non-PGW military personnel. The study instrument consisted of validated questions, validated questionnaires, and investigator-derived questions designed to assess relevant medical and psychiatric conditions. Population-based sample of military personnel from Iowa. A total of 4886 study subjects were randomly selected from 1 of 4 study domains (PGW regular military, PGW National Guard/Reserve, non-PGW regular military, and non-PGW National Guard/Reserve), stratifying for age, sex, race, rank, and branch of military service. Self-reported symptoms and symptoms of medical illnesses and psychiatric conditions. Overall, 3695 eligible study subjects (76%) and 91% of the located subjects completed the telephone interview. Compared with non-PGW military personnel, PGW military personnel reported a significantly higher prevalence of symptoms of depression (17.0% vs 10.9%; Cochran-Mantel-Haenszel test statistic, P<.001), posttraumatic stress disorder (PTSD) (1.9% vs 0.8%, P=.007), chronic fatigue (1.3% vs 0.3%, P<.001), cognitive dysfunction (18.7% vs 7.6%, P<.001), bronchitis (3.7% vs 2.7%, P<.001), asthma (7.2% vs 4.1%, P=.004), fibromyalgia (19.2% vs 9.6%, P<.001), alcohol abuse (17.4% vs 12.6%, P=.02), anxiety (4.0% vs 1.8%, P<.001), and sexual discomfort (respondent, 1.5% vs 1.1%, P=.009; respondent's female partner, 5.1% vs 2.4%, P<.001). Assessment of health-related quality of life demonstrated diminished mental and physical functioning scores for PGW military personnel. In almost all cases, larger differences between PGW and non-PGW military personnel were observed in the National Guard/Reserve comparison. Within the PGW military study population, compared with veterans in the regular military, veterans in the National Guard/Reserve only reported more symptoms of chronic fatigue (2.9% vs 1.0%, P=.03) and alcohol abuse (19.4% vs 17.0%, P=.004). Military personnel who participated in the PGW have a higher self-reported prevalence of medical and psychiatric conditions than contemporary military personnel who were not deployed to the Persian Gulf. These findings establish the need to further investigate the potential etiologic, clinical, pathogenic, and public health implications of the increased prevalence of multiple medical and psychiatric conditions in populations of military personnel deployed to the Persian Gulf.