A review of clinical observations and literature reports leads to the hypothesis that, via a process analogous to Sydenham's chorea, infections with group A beta-hemolytic streptococci, among others, may trigger autoimmune responses that cause or exacerbate some cases of childhood-onset obsessive-compulsive disorder (OCD) or tic disorders (including Tourette's syndrome). If this hypothesis is correct, then immunological treatments should lead to decreased symptoms in some cases. Four cases with abrupt, severe onset or worsening of OCD or tics are presented from an open treatment study. All were boys aged 10 to 14 years. One had OCD, one had Tourette's syndrome, and two had both OCD and Tourette's syndrome. Clinically and on standardized rating scales, their symptoms were in the moderate to very severe range. Two had evidence of recent group A beta-hemolytic streptococci infections, and the others had histories of recent viral illnesses. Two were treated with plasmapheresis, one with intravenous immunoglobulin, and one with immunosuppressive doses of prednisone. All had a clinically significant response immediately after treatment. Diagnostic criteria are provided that describe these cases of pediatric, infection-triggered, autoimmune neuropsychiatric disorders (PITANDs). Suggestions are made regarding the evaluation and management of patients who may have this condition.