The 20-item Leyton Obsessional Inventory--Child Version was completed by children and adolescents who had had Sydenham's chorea (N = 23) or rheumatic fever without chorea (N = 14). The Sydenham's chorea subjects had significantly more obsessive thoughts and compulsive behaviors and significantly greater interference from these behaviors. Three Sydenham's chorea patients but no rheumatic fever patients had substantial obsessional interference and met criteria for obsessive-compulsive disorder when interviewed by telephone. This suggests that obsessive-compulsive disorder, at least in some patients, may be due to basal ganglia dysfunction.