Patterns of cimetidine use were identified in a survey of 3032 patients in 31 nursing homes. Of these, 60 (2%) were receiving cimetidine. For these patients, ages ranged from 63 to 102 years (mean, 81 years). The patients received a range of 1 to 11 regularly scheduled medications (mean, 5.6 medications). Duration of cimetidine treatment averaged 19.6 months for 48 patients (81%) receiving the drug for longer than an eight-week course of therapy. Prescribing indications appeared unjustified in 54 of 60 patients (90%). Doses were rarely appropriately reduced for patient age, despite established reasons to do so and the well-known potential for adverse effects of cimetidine in the elderly. The risks associated with prolonged drug-induced suppression of gastric acid are not known. This study suggests that use of cimetidine without justifiable indication and for extended periods of time is common in nursing home patients. Studies are needed concerning the safety of long-term cimetidine use in elderly patients.