Exposure and ritual prevention (EX/RP) is an effective treatment for obsessive compulsive-disorder (OCD), although it is neither universally nor completely helpful. Compliance with EX/RP treatment procedures has been linked theoretically to posttreatment outcome, yet empirical exploration of this relationship has been insufficient. In this study, therapists were asked to rate the treatment compliance of 28 consecutive patients who received EX/RP on a fee-for-service basis. Results indicated that understanding the treatment rationale and compliance with in-session and homework exposure instructions, but not with ritual prevention and self-monitoring of rituals, was significantly related to posttreatment OCD symptom severity. Clinical implications of these findings and future directions in treatment compliance research with OCD patients are discussed.