We evaluated cognitive dysfunction in Behçet's disease (BD) with and without neurological manifestations by P300 and neuropsychological tests. Thirty-four BD patients without neurological manifestations, eighteen BD patients with neurological manifestations and 15 controls were studied. P300 potentials and neuropsychological tests were performed. P300 latency values and neuropsychological tests were not significantly different from the normal controls in BD patients without neurological manifestations. In neurologically symptomatic patients attention and memory deficits and delayed P300 potentials were found.