The autism spectrum has become a highly studied topic, perhaps the most researched of all developmental disorders. A host of related topics are being studied, with one of the most common being comorbidity of autism with other conditions such as epilepsy, sleep, and anxiety disorders. One of the most prevalent of these comorbid conditions is attention-deficit/hyperactivity disorder (AD/HD). A considerable amount of research has appeared on this topic with respect to symptom expression, prevalence of overlap, type of symptom overlap, and the effect of these two conditions co-occurrence on other symptoms and disorders. Given the substantial data base that has accrued, review and synthesis of these data are in order. This is the purpose of the present manuscript.