Although Attention Deficit/ Hyperactive Disorder (ADHD) is a common comorbidity in individuals diagnosed with Substance Use Disorder (SUD), little data currently exists on the utility of screening tools in large samples of adult patients with SUD in inpatient treatment. This was a 10-week, 2-phase, open label trial of atomoxetine for ADHD in adult patients being treated for a co-morbid SUD in a residential treatment facility (RTF). The primary objective of the study was to assess the efficacy of atomoxetine in adults with an SUD and ADHD. Secondary objects included assessment of the co-morbidity of ADHD and the safety and tolerability of atomoxetine in this population.