While a sizeable subgroup of children with ASD also experience symptoms of over activity and inattention, there have been relatively few randomized clinical trials of pharmacology, especially in combination with behavioral therapy, for attention-deficit/hyperactivity (ADHD) in children with autism spectrum disorders (ASD). Studies involving stimulant medications have generally found poorer response rates and higher rates of intolerable side effects than in typically developing children with ADHD. Atomoxetine (Strattera) – a nonstimulant that affects the norepineprine system – was approved by the FDA in January 2003 for treatment of ADHD, but the relative effectiveness of atomoxetine in ASD and in combination with evidence-based behavioral interventions has not been well examined. In this project, researchers will perform a double-blind, placebo-controlled, 10-week parallel-group comparison of atomoxetine (ATX) versus placebo in ASD children with ADHD. In a separate but parallel study, the researchers will also assess the effectiveness of combining ATX treatment with a standard behavioral intervention paradigm known as Parent Management Training (PMT), which alone has been shown to be useful in managing ADHD symptoms. Children with ASD have been neglected in pharmacological research, placing an enormous burden on health care and educational systems. This trial has the potential to provide answers regarding optimal treatment (both behavioral and pharmacological) for a sizeable subgroup of children with ASD who experience symptoms of over activity and inattention.