A subgroup of patients with childhood-onset obsessive-compulsive disorder (OCD) has been identified who share a common clinical course characterized by dramatic symptom exacerbations following Group A beta-hemolytic streptococcal (GABHS) infections. The term PANDAS has been applied to the subgroup, to indicate the postulated etiology of their symptoms: Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections. Five clinical characteristics define the PANDAS subgroup: presence of OCD and/or tic disorder, prepubertal symptom onset, sudden onset or abrupt exacerbations (sawtooth course), association with neurological abnormalities (presence of adventitious movements or motoric hyperactivity during exacerbations), and temporal association between symptom exacerbations and GABHS infections. Post-streptococcal symptom exacerbations are typically quite dramatic, with patients reporting that their symptoms "...came on overnight" or "...appeared all of a sudden a few days after I had a sore throat." The post-streptococcal inflammatory nature of the neuropsychiatric symptoms provides novel opportunities for treatment and prevention, including immunomodulatory therapies such as therapeutic plasma exchange (TPE) and intravenous immunoglobulin (IVIG). A recently completed placebo-controlled trial revealed that both IVIG and TPE were effective in reducing neuropsychiatric symptom severity (40% to 55% reductions, respectively) for a group of severely ill children with OCD and/or tic disorders. Further research is required to determine why the treatments are helpful, as well as to ascertain whether or not antibiotic prophylaxis can help prevent post-streptococcal symptom exacerbations.