Objective: In the present study, subclinical lesion involvement was investigated using the P50 component in Behçet's patients without neurological manifestation. Methods: We performed this clinical research in Erciyes University, Faculty of Medicine between December 2000 and November 2001. The studies were carried out on 18 Behçet's patients without neurologic findings and 18 volunteers for control. Standard Ag/AgCl electrodes in plastic cups were used for monopolar EEG derivations. They were attached with electrode paste and tape at the Cz (vertex) according to the 10-20 system. The auditory stimuli were delivered in pairs. The P50 waves, which may be taken from approximately 50 msec from the stimuli, were collected by computer system. Amplitudes and latencies of the P50 components were measured in the same system. Results: This study showed that the suppression of P50 responses performed by the test stimuli, was significantly more decreased in Behçet's patients than the control subjects. Conclusion: The decrease of the suppression of the auditory P50 response to repeated stimuli reflects a deficit in the central nervous system's ability, such as attention, cognition, and sensory input in Behçet's patients and can be used as a neurophysiological marker in subclinical lesions in these patients.