A comprehensive classification of motor disorders attributed to neuroleptic drugs is proposed. Some manifestations resemble those occurring in known diseases of the central nervous system; other abnormalities are typical effects of drugs with neuroleptic action. A factor analysis on the most frequently occurring motor disorders generated the following symptom clusters: (1) tremor, bradykinesia, rigidity, and attendant symptoms; (2) buccolingual-masticatory dyskinesia, astasia, dyskinesia of the lower extremities and posture in extension; and (3) dyskinesia of the upper extremities and postural disorder. The classification and the factors were used to study the effects of drug withdrawal on a sample of patients over a sixmonth period. Symptoms of cluster 1 decreased while those of cluster 2 increased in severity. In a control group receiving standard drugs during a comparable period, no significant changes were noted.