The purpose of this study was to examine the efficacy and side-effects of pindolol, a β-blocker, in children with attention-deficit hyperactivity disorder (ADHD). Fifty-two ADHD children, 7–13 years old, participated in a prospective double-blind placebo-controlled comparison of pindolol and methylphenidate (MPH). Active treatment was pindolol and MPH: pindolol 20 mg b.i.d. or MPH 10 mg b.i.d. for 4 weeks. The outcome was assessed on the basis of the Abbreviated Conners Rating Scales (ACRS) completed by parents, teachers, and by a psychologist during psychological testing. Pindolol treatment was associated with a higher incidence of paraesthesias and with more intense nightmares and hallucinations than MPH or placebo treatment. These side-effects led to an interim change in design by ending pindolol treatment after 32 participants. Pindolol proved to be just as effective as MPH in decreasing hyperactivity and conduct problems at home, and hyperactivity problems at school. Pindolol, however, had less therapeutic effects than MPH during psychological testing, and failed to affect conduct problems in school. In sum, pindolol was modestly effective in the treatment of ADHD. Safety concerns on troubling side-effects clearly limit the use of it.