The Diagnostic and Statistical Manual of Mental Disorders (4th Edition) prohibits the co-diagnosis of attention-deficit/hyperactivity disorder (ADHD) and an autism spectrum disorder (ASD). However, recent studies indicate that co-occurrence of clinically significant ADHD and autistic symptoms is common, and that some genes may influence both disorders. Children with the combination of ADHD and motor coordination problems are particularly likely to have an ASD. These co-occurrences of symptoms are important since children with ASD in addition to ADHD symptoms may respond poorly to standard ADHD treatments or have increased side effects. Such children may benefit from additional classes of pharmacologic agents (i.e., alpha-agonists, selective serotonin reuptake inhibitors and neuroleptics). They may also benefit from social skills therapy, individual and family psychotherapy, behavioral therapy and other nonpharmacologic interventions.