The 143 physicians who returned to Temple University Medical School a questionnaire on knowledge of prescribing for the elderly constituted 25% of a stratified random sample of general practitioners (GPs), family practitioners (FPs), and practitioners in internal medicine (IMs) reimbursed under Medicare in Pennsylvania in 1979. The mean score on the 23-item drug questionnaire was significantly lower (P less than .05) than the score deemed adequate by a panel of six experts in the field. Five variables, identified by survey questions, were positively associated with physicians' test scores: importance of professional meetings, perception of need for continuing medical education, board eligibility/certification, group practice, and a practice in which the elderly constitute 25 to 49% of all patients. Two variables were negatively associated: number of years since date of licensure and the importance of drug advertisements. Respondents and nonrespondents were compared on nine variables for which American Medical Association (AMA), American Osteopathic Association (AOA), or Blue Shield data were available. Pennsylvania graduates were significantly overrepresented in the respondent group. The only other significant difference found was in field of practice, where findings differed by source of information. There was no significant difference in mean scores of early and late respondents. The research findings support those of three previous studies, not limited to the elderly, which found prescribing knowledge inadequate. They suggest the need for examining/improving the opportunities for medical students and physicians to increase their knowledge of geriatric pharmacology.