The association between Tourette syndrome, attention-deficit hyperactivity disorder (ADHD), and obsessive-compulsive disorder following streptococcal infections has been documented, but with conflicting reports. We thus felt it was important to investigate this association in a group of Italian patients not previously documented. We took blood on 69 patients with Tourette syndrome and 72 age- and sex-matched tic-free controls. Laboratory staff were blind to the diagnostic status of the subjects. Evidence of recent streptococcal infection was defined using antistreptolysin titers. Anti-basal ganglia antibodies were determined using human basal ganglia sections. Statistical analysis was conducted using analysis of variance and chi-square tests. Raised antistreptolysin titers were found in 41 of 69 (59%) patients with Tourette syndrome and 14 of 72 (19%) controls (P = .000). Positive anti-basal ganglia antibodies were found in 22 of 69 (32%) subjects with Tourette syndrome compared with 7 of 72 (10%) controls, which was also significant (P = .002). Raised antistreptolysin titers were detected in 18 of 22 (82%) patients with Tourette syndrome with positive anti-basal ganglia antibodies and 22 of 47 (47%) patients with negative anti-basal ganglia antibodies (P = .01). These results support the reported association between streptococcal infection and anti-basal ganglia antibodies and some patients with Tourette syndrome.