The potential for anticholinergic toxicity due to concurrent use of medications was assessed among 5,902 continuous nursing home residents and a comparable group of ambulatory patients. During the study year nearly 60% of the nursing home residents and 23% of the ambulatory patients received drugs with anticholinergic properties. Based on recommended doses of the drugs, 565 of the nursing home patients and 413 of the ambulatory patients could have received three or more anticholinergic medications concurrently. An examination of nursing home patients receiving the most frequently prescribed antipsychotic and tricyclic antidepressant drugs concurrently revealed that physicians did not choose drugs selectively within the two classes in order to minimize the potential for anticholinergic toxicity. The findings of this study suggest that the risk of anticholinergic toxicity may be underestimated by physicians.