Objective: To evaluate the effectiveness of dronabinol (delta-9-THC) as supplementary therapy in a child with autistic disorder. Methods: A child who met the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) criteria for a diagnosis of autistic disorder and who took no other medication during the observation time was included in an open and uncontrolled study. Symptom assessment was performed using the Aberrant Behavior Checklist (ABC) before and after six months of medical treatment. Result: Compared to baseline, significant improvements were observed for hyperactivity, lethargy, irritability, stereotypy and inappropriate speech at follow-up (p=0.043). Conclusion: This study showed that the use of dronabinol may be...