Cognitive-behavioral therapy (CBT) is an effective treatment for childhood obsessive-compulsive disorder (OCD). However, no case studies of children younger than 7 years old have been published. This case report describes a 5-year-old boy with severe OCD. Treatment consisted of parent-and teacher-directed extinction of compulsive reassurance-seeking, and bibliotherapy with an age-appropriate book on OCD. Compulsive behavior decreased rapidly and remained at a low level through the remainder of treatment. At posttreatment and at 1-and 3-month follow-up assessments, the patient’s OCD symptoms were markedly improved. This report suggests that very young children may respond well to brief CBT.