ABSTRACT.Elderly people tend to be large consumers of medication in general and psychotropic drugs in particular. Sedative/hypnotics, anxiolytics, antidepressants, and neuroleptic drugs tend to be the most commonly used psychotropic medications among elderly people who are not developmentally disabled. These drugs are probably commonly employed among elderly mentally retarded people as well; although the rank order of use probably differs. A number of physiological changes which accompany greater age are described and the impact on pharmacokinetic variables outlined. Other factors associated with aging, which influence drug actions, are also outlined. The net effect appears to be that most drugs are more potent, more toxic, or longer lasting among the elderly. Data are also presented on tardive dyskinesia insofar as aging is concerned. This is followed by overall conclusions and some suggested guidelines for the use of these drugs in older mentally retarded persons.