Obsessive-compulsive disorder (OCD) is characterized by engagement in rituals that serve to obtain certainty and prevent feared outcomes. Exposure and response prevention is most effective when rituals are resisted, yet existing self-report measures of OCD limit identification of the full range of possible rituals, and little is known about how rituals might cluster together and predict worsened severity and poorer treatment outcomes. In a retrospective sample of 641 adult patients who received intensive OCD treatment, the present study used a mixed-methods approach to (a) identify and validate treatment provider-identified rituals using the Yale-Brown Obsessive-Compulsive Scale, (b) identify clustering patterns of rituals, and (c) examine the impact of these clusters on severity and treatment outcomes. Sixty-two discrete rituals clustered into eight higher order ritual clusters: avoidance, reassurance, checking, cleaning/handwashing, just right, rumination, self-assurance, and all other rituals. At admission, reassurance predicted greater intolerance of uncertainty (IU) and rumination predicted less OCD severity. Only one ritual cluster-just right-predicted treatment outcomes; patients with just right rituals had worse IU at discharge and significantly longer length of treatment (average 7.0 days longer). Clinical observation can identify more nuanced and individualized rituals than self-report assessment alone. Patients presenting with just right rituals may benefit less from treatment focused on harm avoidance and habituation; instead, treatment should be tailored to the idiosyncrasies of incompleteness and not just the right experiences. (PsycInfo Database Record (c) 2023 APA, all rights reserved).