Hoarding frequently occurs in obsessive-compulsive disorder (OCD), and some evidence suggests that it constitutes a distinct OCD subtype, with genetic contributions. This study investigated differences between OCD patients with and without hoarding symptoms. Of the 473 OCD patients studied, 24% were classified as hoarders according to combined interviewer and self-ratings, which were validated with the Savings Inventory-Revised in a subsample. Hoarders suffered from significantly more severe OCD symptoms, (especially compulsions) and had greater impairment and dysphoria. Hoarders also had more comorbid psychiatric disorders. Further study revealed that many of these differences were attributable to the female subjects: Compared to female non-hoarders, female hoarders were more likely to suffer from bipolar I, substance abuse, panic disorder, binge-eating disorder, and had greater OCD severity. Male hoarders had an increased prevalence of social phobia compared to non-hoarding males. These results suggest that there are gender-specific differences in the hoarding sub-phenotype of OCD.