Although a diagnosis of obsessive-compulsive disorder (OCD) can be made with the specification "poor insight" (PI), this subtype remains understudied. To investigate the subtype, 78 OCD patients were characterized by degree of insight, reevaluated after treatment, and compared with 20 schizophrenics with OCD (OCD+S). At the pretreatment assessments in OCD patients, 28 subjects with poor or delusional insight (PI; 36%) were distinguished from 50 subjects with fair or good insight (GI; 64%) using the insight question of the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). Compared to the OCD+S group, OCD patients were less likely to have PI, whereas OCD PI patients showed a similar degree of functional impairment as that observed in the OCD+S. After a 6-month combination of clomipramine with cognitive-behavioral treatment, 14 of 25 OCD PI patients no longer fell in the PI category, which was associated with reduced OCD severity and depressive status. Schizotypal personality disorder (SPD) was more common in patients whose insight remained poor even after the treatment. OCD patients demonstrate a range of insight with PI accompanied by significant dysfunction. Comorbid SPD in PI patients may be associated with worse prognosis.