Little is known about longitudinal prescribing practices for psychoactive medications for individuals with intellectual disabilities and developmental disabilities (IDDD) who are living in community settings. Computerized pharmacy records were accessed for 2344 community-based individuals with IDDD for whom a total of 3421 prescriptions were written during a 17-month period of study. Forty-two psychoactive medications were rank ordered in terms of prescription frequency. Fifty-two per cent (52%) of all prescriptions written during the study period were for psychoactive medications. Anticonvulsant, antipsychotic and antidepressant medications were the most commonly filled prescriptions among psychoactive medications. Sixty per cent (62%) of the study population was given prescriptions for more than one psychoactive medication and 36% received three or more psychoactive medications. During the study period, there was a statistically significant increase in prescriptions filled for olanzapine, risperidone, valproic acid, and clonazepam whereas prescriptions filled for thioridazine, haloperidol, and benzotropine showed a significant decline (P<0.050.001). Distribution of psychoactive drug class by age showed that the majority of prescriptions were filled for individuals between 20 and 50 years with the exception of prescriptions for psychostimulants which peaked for individuals prior to 20 years. (1) Analysis of pharmacy billing records provides a method for assessing prescribing patterns of psychoactive medications in community-based individuals with IDDD. (2) Polypharmacy for psychoactive medications is prevalent in this setting. (3) The second-generation antipsychotic medications are prominently represented by an increasing number of filled prescriptions during the study period.