Cognitive-behavioral therapy (CBT) with exposure and response prevention is known to be effective in the treatment of older youth (8-17) and adults with obsessive-compulsive disorder (OCD); however, very little is known about the effectiveness of these procedures during early childhood. As such, this case describes the application of a modularized family-based CBT approach focusing on exposure, differential reinforcement of other behaviors (DRO), and reductions in family accommodation with a preschool boy with a primary diagnosis of OCD. Following 12 consecutive family sessions over 6 weeks, “Charley,” a 4-year-old Caucasian male, showed substantial reductions in OCD symptomatology. Charley’s parents also reported improvements in oppositionality, peer functioning with siblings and at preschool, and in the parent–child relationship. All improvements were maintained at 3-month follow-up. These results provide preliminary support that CBT incorporating exposure, DRO, behavioral parent training, and reductions in family accommodation may be effective for preschoolers with OCD.