Factors associated with the emergence or nonemergence of involuntary movements (tardive dyskinesia) during long-term neuroleptic treatment were investigated in an atypical, isolated population of 31 schizophrenic inpatients with an unusually high prevalence of this syndrome. Patients with involuntary movements could not be distinguished from those without such movements by general characteristics or conventional indices of neuroleptic or anticholinergic treatment. However, they were more likely to show either marked cognitive dysfunction or muteness. These findings support the proposal that, at least in schizophrenia, subtle organic changes may contribute to vulnerability to the emergence of involuntary movements.