Pediatric autoimmune neuropsychiatric disorders associated with streptococcal infection (PANDAS) is a relatively new diagnostic construct applied to children or adolescents who develop, and have repeated exacerbations of, tic disorders and/or obsessive-compulsive disorder following group A beta-hemolytic streptococcal infections. The proposed pathophysiology is that the group A beta-hemolytic streptococcal bacteria trigger antibodies that cross-react with the basal ganglia of genetically susceptible hosts leading to obsessive-compulsive disorder and/or tics. This is similar to the etiologic mechanisms proposed for Sydenham's chorea, in which group A beta-hemolytic streptococcal antibodies cross-react with the basal ganglia and result in abnormal behavior and involuntary movements. When first proposed, there was much controversy about the idea that streptococcal infections were etiologically related to rheumatic fever. In a like manner, discussion has arisen about the concept of infection-triggered obsessive-compulsive disorder and tic disorders. We review the historical background to these controversies, give an update on the findings provided by research on PANDAS, and address areas of future study. (J Child Neurol 1998; 13:413-423).