While there have been several reports concerning the treatment of inappropriate sexual behaviors in children with autism spectrum disorder (ASD), there have been no reports concerning treatment of childhood masturbation in subjects with ASD aged <3 years. We describe a 30-month-old girl referred to our department due to language delay, behavioral problems, and lower-limb contractions. She was diagnosed with ASD according to the Diagnostic and Statistical Manual of Mental Disorders (5th Edition) criteria and with early childhood masturbation according to the 10th revision of the International Statistical Classification of Diseases and Related Health Problems. Escitalopram was added to treatment when behavioral methods proved insufficient to resolve the masturbatory behavior and due to the patient’s young age. The masturbatory behavior resolved entirely 3 weeks after the start of escitalopram treatment. We wish to report the first case of masturbation under the age of 3 successfully treated with escitalopram.