Assessed measures of psychological and neurobehavioral functioning to determine their association with unexplained symptoms in Gulf War veterans. Persistent symptoms with no medical explanation associated with service in the Persian Gulf (e.g., fatigue, muscle pain, and memory deficits) that began during or after the war qualified respondents as cases. The 241 veterans (mean age 34.3 yrs) with unexplained symptoms were classified as case Ss, and the 113 veterans without symptoms were classified as control Ss. All veterans completed a battery of computerized assessment tests consisting of 12 psychosocial and 6 neurobehavioral tests. Case Ss differed substantially and consistently from control Ss on diverse psychological tests in the direction of increased distress and psychiatric symptoms. Case Ss had small but statistically significant deficits relative to control Ss on some neurobehavioral tests of memory, attention, and response speed. The results revealed that Gulf War veterans who report symptoms associated with that conflict differed on multiple psychological measures in the direction of increased distress and performed more poorly on neurobehavioral measures when compared with control Ss who did not report symptoms.