Twenty-three unmedicated patients with obsessive-compulsive disorder (OCD) were compared with 12 unmedicated patients with social phobia (SP) and 18 age-matched normal controls (C) using a two-tone auditory oddball event-related potentials (ERP) paradigm. The OCD group showed significantly shorter P300 latencies and shorter N200 latencies for target stimuli than the SP and the C groups. The OCD patients also tended to have greater N200 negativity compared with normal controls. However, there were no significant relationships between these ERP abnormalities in OCD patients and the type or severity of their OCD symptoms. In the mean ERP waveforms, increased N200 negativity for target stimuli, as well as the provocation in the later part of N200 for non-target stimuli, were more commonly observed in the OCD and the SP groups compared with the C group. These results raise the possibility that the shorter N200 and P300 latencies in OCD patients may be an OCD-specific phenomenon that is more closely related to the biological basis for OCD, rather than the characteristics of their OCD symptoms. On the other hand, increased negativity in the N200 region, even for non-target stimuli, may represent the common abnormalities among anxiety disorders.