This longitudinal study examined whether specific cognitive patterns during pregnancy predict postpartum obsessive-compulsive (OC) symptoms. A diverse sample of 256 women was assessed at 20 weeks of pregnancy (Time 1), 6 weeks postpartum (Time 2; n = 233), and 6 months postpartum (Time 3; n = 231). At each point, participants completed interview and/or self-report measures of OC symptoms, psychological distress, and obsessive beliefs (i.e., cognitive patterns related to OC symptoms). Postpartum OC symptoms were common, reported by 87.1 % at Time 2 and 74.5 % at Time 3. Stronger prenatal obsessive beliefs during pregnancy predicted greater postpartum OC symptom severity and higher likelihood of an OCD diagnosis at Time 3, even after controlling for baseline OC symptoms and distress. Findings highlight the clinical importance of prenatal cognitive risk factors and support cognitive-behavioral models of postpartum OCD.