ABSTRACT.The prevalences and inter‐relationships of five types of movement disorders were evaluated in a large, developmentally disabled (DD) population (n=1227); prevalence was evaluated with regard to severity, age, gender and antipsychotic‐drug (APD) exposure. Dyskinesia was found in 48% of the sample, dystonia in 29%, akathisia in 13%, Parkinsonism in 3% and paroxysms in 4%. Many persons had more than one symptom so that 72% had one or more of the five target symptoms. Although the five movement‐disorder categories were not mutually exclusive, analysis supported the individuality of the categories as defined in this study. The prevalences of dyskinesia and Parkinsonism were considerably greater than those in the general population. On the other hand, the prevalence of dyskinesia was similar to that reported for psychiatric and institutionalized geriatric populations. Parkinsonism increased with age and male gender, while dyskinesia increased with age and female gender. APD‐exposure was significantly correlated only with ak