OCD affects nearly 1% of the pediatric population. The symptoms of this illness can interrupt development, causing significant psychological distress and producing life-long impairments in social, academic, and occupational functioning. A subgroup of pediatric OCD has been designated by the acronym PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections). This type of OCD is characterized by sudden symptom onset and a relapsing-remitting course of illness; exacerbation of symptoms occurs with scarlet fever or strep. throat infections. This study will identify factors that distinguish children with PANDAS OCD from children with non-PANDAS OCD, and will compare both groups to healthy children.