The occurrence of acute dystonic reactions was intensively monitored in a population of 646 patients, 379 males and 267 females, aged 18-87 years, consecutively admitted to different psychiatric units and treated with neuroleptics alone or in combination with anticholinergic drugs. Thirty-four patients experienced acute dystonic reactions yielding a total incidence of 5.3%. There was a tendency towards a higher frequency of dystonia in males than in females, and in young patients than in older ones. Patients without anticholinergic medication had a higher frequency of the reaction than those receiving anticholinergic drugs (8.5% vs. 2.8%; p < 0.02). Neuroleptic-induced dystonia was more common in patients treated with butyrophenones than in those receiving phenothiazines or substituted benzamides.