In this study we investigated predictors of utilization of primary care physician, hospital and emergency room services in a sample of 909 older patients during the first year following a diagnosis of cancer of the breast, colon, lung, or prostate. Analysis of covariance models were implemented separately for the active treatment period (0-6 months) and the continuing care period (6-12 months) to determine how age, sex, comorbidity, length of survival, treatment status, stage of disease, cancer site, physical functioning, and symptom count were related to primary care physician visits, hospitalization, and emergency room use. Decreased physical functioning was related to increased physician visits, hospital nights, and emergency room visits during the active treatment period, and to increased hospital nights and emergency room visits during the continuing care period. Patients with three or more comorbid conditions reported more physician visits than patients with no comorbid conditions during both periods. Patient age did not play a significant role in utilization of services. The broad picture suggested by this study of elderly cancer patients is that their service utilization, particularly hospitalization and emergency room services, tends to peak in concert with a dramatic decrease in physical functioning as the patient nears the end of life. Use of primary care physicians' services may depend substantially on comorbid conditions.