Objective: Previously, data from 97 weeks of open-label atomoxetine treatment of adults with attention-deficit/hyperactivity disorder (ADHD) were reported. This final report of that study presents results from over 4 years of treatment. Method: Results were derived from the study of 384 patients (125 patients remaining in the open-label trial since the interim report), receiving up to 221 weeks of treatment. Primary efficacy measure was the Conners' Adult ADHD Rating Scale-Investigator Rated: Screening Version (CAARS-Inv:SV) Total ADHD Symptom score. Adverse events and vital signs were assessed. Results: CAARS-Inv:SV Total ADHD Symptom scores decreased 30.2% (p less than 0.001) during treatment. Similar, significant decreases were noted for the secondary efficacy measures, including the Sheehan Disability Scale Total score, which improved 25.3% (p less than 0.001). Adverse events consisted primarily of pharmacologically (noradrenergic) expected effects. Conclusions: Results of this open-label study support the long-term efficacy, safety, and tolerability of atomoxetine for the treatment of adult ADHD. (Contains 3 tables.)