Overestimation of threat (OET) has been implicated in the pathogenesis of obsessive-compulsive disorder (OCD). The present study deconstructed this complex concept and looked for specific deviances in OCD relative to controls. A total of 46 participants with OCD and 51 nonclinical controls were asked: (a) to estimate the incidence rate for 20 events relating to washing, checking, positive, or negative incidents. Furthermore, they were required (b) to assess their personal vulnerability to experience each event type, and (c) to judge the degree of accompanying worry. Later, participants were confronted with the correct statistics and asked (d) to rate their degree of worry versus relief. OCD participants did not provide higher estimates for OCD-related events than healthy participants, thus rendering a knowledge deficit unlikely. The usual unrealistic optimism bias was found in both groups but was markedly attenuated in OCD participants. OCD-related events worried OCD participants more than controls. Confrontation with the correct statistics appeased OCD participants less than healthy participants. Even in the case of large initial overestimations for OCD-related events, correct information appeased OCD participants significantly less than healthy participants. Our results suggest that OCD is not associated with a knowledge deficit regarding OCD-related events but that patients feel personally more vulnerable than nonclinical controls. (Contains 2 tables and 1 figure.)