The primary purpose of this study was to describe tolerability and efficacy of venlafaxine in the treatment of children and adolescents with attention deficit hyperactivity disorder (ADHD). A 6-week open trial of venlafaxine was conducted in 13 children and adolescents (mean age 9.9 +/- 2.5 years) with ADHD, and without comorbid depression. Venlafaxine was initiated at a dose of 18.75 mg/day and flexibly titrated to 56.25 mg/day. The Conners parent scale and Clinical Global Improvement (CGI) severity item were performed at baseline and at the end of the 6-week trial. All subjects completed the trial. Mean final dose of venlafaxine was 40.3 +/- 7.0. Venlafaxine was significantly effective in reducing the total score of the Conners parent scale from baseline to endpoint (P < 0.002, Z =-3.113) and the CGI severity item (P < 0.05). Transient side-effects such as somnolence (n = 2), stomachache (n = 2), and headache (n = 1) disappeared after second week of treatment. Also three subjects complained of sedation after raising the dose to 56.5 mg/day, therefore the dose was reduced to the previous level. These preliminary data suggest that venlafaxine may be an effective medication in the treatment of some children and adolescents with ADHD. Future double-blind controlled trials should be undertaken.