Personality differences between 'washer' and 'checker' subtypes of obsessive-compulsive disorder (OCD) were explored. Fifty-one OCD patients were recruited from several outpatient clinics in Central Israel. OCD was diagnosed according to DSM-III-R using the Structured Clinical Interview for DSM-III-R, and personality disorders were diagnosed using the Structured Clinical Interview for DSM-III-R Personality Disorders. Washers were much more likely to have personality disorders than checkers. Personality disorders were diagnosed in 12 of 13 washers vs. three of 11 checkers (chi 2 = 10.75, Fisher's exact test, P < 0.001, d.f. = 1, odds ratio = 32, CI = 2.8-365) and 21 of 27 patients with mixed OCD symptoms. The results support the validity of the washer-checker subdivision and might explain the relative refractoriness of washers to conventional intervention.