Multisymptom illness is more prevalent in 1991 Gulf War veterans than in military comparison groups; less is known about comorbidities. The authors compared physical, psychological, and functional comorbidities in Australian male Gulf War I veterans with those in actively (non-Gulf) deployed and nondeployed military personnel by using a questionnaire and medical assessment in 2000-2002. Multisymptom illness was more common in male Gulf War veterans than in the comparison group (odds ratio (OR) = 1.80, 95% confidence interval (CI): 1.48, 2.19). Stratifying by deployment status in the comparison group made little difference in this association. Gulf War veterans with multisymptom illness had increased psychiatric disorders, including major depression (OR = 6.31, 95% CI: 4.19, 9.52) and posttraumatic stress disorder (OR = 9.77, 95% CI: 5.39, 18.59); increased unexplained chronic fatigue (OR = 13.32, 95% CI: 7.70, 23.05); and more reported functional impairment and poorer quality of life, but objective physical and laboratory outcomes were similar to those for veterans without multisymptom illness. Similar patterns were found in the comparison groups; differences across the 3 groups were statistically significant for only hospitalization, obstructive liver disease, and Epstein-Barr virus exposure. Multisymptom illness is more prevalent in Gulf War I veterans, but the pattern of comorbidities is similar for actively deployed and nondeployed military personnel.