This case report describes a child with a severe autistic syndrome worsened by hypersexual behavior consisting of compulsive masturbatory activity. Selective serotonin reuptake inhibitors have been reported to be beneficial in reducing hypersexual behaviors. A treatment with mirtazapine improved the entire clinical autistic picture with the disappearance of masturbation. This result suggests that selective serotonin reuptake inhibitors could be useful and promising tools in the treatment of hypersexual behaviors in children with autistic disorders. Moreover, the general, and in some ways unexpected, improvement of the social interaction, communication, and imagination, the dramatic reduction of aloof mannerisms, stereotypes, aggressiveness, and inappropriate emotional response to frustrations, as well as the first appearance of the pragmatic use of language and a strong impetus to emotional development disclosed a new spectrum of possible applications of these drugs, and mirtazapine in particular, suggesting the need for new and more extensive studies on the pharmacotherapy of autism.