purpose: Controversy exists as to whether patient age, either independently or as a marker of concomitant illness or medication use, is associated with the dose or complication rate of warfarin prophylaxis. The aim of this study was to assess this relationship in patients receiving warfarin prophylaxis after hip fracture repair. patients and methods: We undertook a retrospective cohort study of 215 patients 55 years of age or greater who underwent surgery for a fractured hip between January 1, 1990, and December 31, 1991, and received warfarin prophylaxis. The mean age was 78.9 (SD 9.5) years. The average daily warfarin dose, the decrease in hemoglobin in the postoperative period, and the rate of bleeding complications were assessed. results: Elderly patients required a significantly lower average daily warfarin dose than younger patients. This effect persisted even after controlling for the number of medical conditions, number of medications on admission, proportion of time the international normalized ratio (INR) was in therapeutic range, and gender. Postoperative hemoglobin decrease was associated with patient age as well as with the use of antibiotics post-operatively. Factors associated with bleeding complications included a history of alcohol abuse and a smaller proportion of time spent in the targeted anticoagulant range. conclusions: Older age itself and not as a marker for polypharmacy or increased number of medical conditions is associated with lower requirements for warfarin and a greater hemoglobin decrease postoperatively even when the proportion of time the INR fell within the therapeutic range is controlled. Advanced patient age, in this study, was not associated with an increased incidence of bleeding complications.