A previous symptom-based survey of veterans of the 1990-1991 Persian Gulf War suggested a neurological syndrome (blurred vision, loss of balance/dizziness, tremors/shaking, and speech difficulty). The authors conducted the present study to determine whether specific findings could indicate an organic basis for this possible syndrome. They completed an extensive clinical and laboratory evaluation on Gulf War veterans with all 4 symptoms, using 3 comparison groups. A single clinically based neurological syndrome could not be identified. No deployment-related exposure appeared to explain the pattern of symptoms, but this evaluation suggested comorbidities and possibly multiple vaccines as important contributors. Many of the neurological symptoms reported by the studied veterans appear to have an organic basis, but comorbidities must be excluded before researchers can conclude that a definitive syndrome exists.