This study (1) analyzed the type and frequency of signs, symptoms, and ill-defined conditions (SSIDs) among 21,579 consecutive Persian Gulf War veterans with symptoms or health concerns after the war. Demographic data, self-reported exposures, symptoms, and physician-assigned International Classification of Diseases (ICD) primary and secondary diagnoses were recorded. A detailed psychosocial history, including a multidisciplinary discussion, was incorporated for a subset of participants. SSID conditions were primary diagnoses for 17.2% of veterans, and either primary or secondary diagnoses for 41.8%. Although some SSIDs were objective conditions (e.g., sleep apnea), most were simply symptoms. More comprehensive evaluation, especially the multidisciplinary discussion of findings, decreased the frequency of symptoms as diagnoses and increased the number of Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) psychiatric diagnoses. Ill-defined conditions were not associated with particular self-reported exposures or demographic variables. Evidence for a new or unique illness related to wartime exposures did not emerge from this analysis.