Patients with truncal extension dystonia, manifested by involuntary back arching, often associated with pain and severe motor disability, have not consistently responded to pharmacologic agents. We evaluated 4 women and 1 man (mean age, 41.8 years; dystonia duration, 9.8 years) with severe idiopathic (2 patients) or tardive (3 patients) truncal and cervical dystonia. Using electromyographic guidance, we injected botulinum toxin into the paravertebral muscles of the lumbar region in four to six sites using 25–50 U per site. We reevaluated patients 2–4 weeks after injection. The mean dose of botulinum toxin into back muscles was 210 U (range, 150–300 U). By blinded videotape evaluation, objective improvement was found in three patients with a mean truncal dystonia score improving by 37%. Patient evaluation showed improvement in movement ranging from 20–80% (mean, 46%) after botulinum toxin. In all patients with pain as a result of dystonia, there was substantial improvement. None of the patients worsened and no adverse effects occurred. Botulinum toxin injections offer a potent new treatment for truncal dystonia.