Owners who believed they had a horse with self-mutilating behavior were asked to complete a questionnaire to obtain information on the signalment, clinical history, clinical signs, management, and treatment of the condition. Fifty-two owners of 59 horses responded; 2 cases were omitted because an organic cause was determined. Owners also were asked to complete information for unaffected horses on the same farm. Various breeds were affected, and of the 57 horses, 20 were stallions, 31 were geldings, and 6 were mares. Affected horses tended to develop the condition prior to sexual maturity. Clinical signs included glancing or biting at the flank or pectoral areas, bucking, kicking, vocalizing, rubbing, spinning, or rolling. Several management and environmental factors were examined, but none were found to be exclusively related to expression of the disorder. Castration was associated with improvement in 7 of 10 stallions. Medications and changes in management reduced or prevented the behavior in some horses. The syndrome appears to be similar to Tourette's syndrome of human beings.