Obsessive-compulsive disorder (OCD) affects nearly 1% of the pediatric population. The intrusive symptoms of this illness can interrupt normative development, causing significant psychological distress and producing life-long impairments in social, academic, and occupational functioning. Current research supports a neurobiologic model for OCD. Converging lines of evidence suggest that a post-infectious autoimmune-mediated process may be associated with the pathogenesis of some pediatric cases. This subgroup has been designated by the acronym, PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections). The abrupt symptom onset and relapsing-remitting course of illness characteristic of the PANDAS subgroup appears to define a distinct cohort of patients, in whom symptom exacerbations occur synchronously with Group A beta-hemolytic streptococcal (GABHS) infections.