Pervasive doubts are a central feature of obsessive–compulsive disorder (OCD). We have theorized that obsessive doubts can arise in relation to any internal state and lead to compensatory reliance on more discernible substitutes (proxies), including rules and rituals. Previous findings corroborated this hypothesis, but were based on students with high and low OCD tendencies and did not control for anxiety. The present study tested our hypothesis in OCD participants using both anxiety disorders and nonclinical controls. Twenty OCD participants, 20 anxiety disorders participants, and 20 nonclinical participants underwent 2 experimental procedures. In the first, participants had to produce specific levels of muscle tension with and without the aid of biofeedback. In the second, participants were asked to subjectively assess their own muscle tension after viewing preprogrammed false feedback showing either increasing or decreasing levels of muscle tension. As predicted, OCD participants were less accurate than anxiety disorder and nonclinical participants in producing designated levels of muscle tension when biofeedback was not available and more likely to request the biofeedback when given the opportunity to do so. In the false feedback procedure, OCD participants were more influenced by the false biofeedback when judging their own level of muscle tension compared with the 2 controls groups. In both procedures, anxiety disorder participants did not differ from the nonclinical controls. These results support the hypothesis that individuals with OCD have attenuated access to and reduced confidence in their internal states, and that this deficit is specific to OCD and not attributable to anxiety.