“Pure obsessions” or “ruminations” without overt compulsions have traditionally been considered rare. However, several treatment programs around the world have shown that the proportion of patients who do not report overt compulsions ranges from 1.5% to 44%, with a median of 20% (for a review, see Freeston & Ladouceur, 1997). Furthermore, epidemiological studies have demonstrated that the proportion of cases of OCD suffering from pure obsessions in the community may be very high, even up to 50%–60% (Weissman et al., 1994). Common themes for obsessions refer to harming, sexuality, contamination, concerns with illness or disease, religion, concerns about mental processing, superstition (e.g., lucky and unlucky numbers), or otherwise neutral thoughts (“What if I cannot stop thinking about my breathing?”). The thoughts are usually egodystonic, but not all patients are convinced that the thoughts are irrational (see Kozak & Foa, 1994). Although the patients do not engage in any overt compulsions, they often engage in avoidance behavior or mental rituals, such as replacing a bad thought with a good one, silent prayer, or mentally reviewing events. Ruminations can be just as incapacitating as compulsions (Solyom, Ledwidge, & Solyom, 1986), and a major shortcoming of the treatmentoutcome studies published in the past 20 years is that they mainly examined OCD patients with overt rituals, usually of the checking or cleaning type (Ball, Baer, & Otto, 1996). Success with behavioral treatments for patients suffering from pure obsessions is variable (e.g., Beech & Vaughn, 1978; Foa, Steketee, & Ozarow, 1985). From Massachusetts General Hospital and Harvard Medical School. Contact author: Sabine Wilhelm, PhD, OCD Clinic, Department of Psychiatry, Massachusetts General Hospital, Building 149, 13th Street, Charlestown, MA 02129. E-mail: wilhelm@psych.mgh.harvard.edu.