BACKGROUND: The elderly utilize emergency medical services (EMS) at a higher rate than younger patients, yet little is known about the influence of injury on subsequent EMS utilization and costs. OBJECTIVE: To assess injury hospitalization as a potential marker for subsequent EMS utilization and costs by Medicare patients. METHODS: This observational study analyzed a retrospective cohort of all Medicare patients (> or = 67 years old) with an International Classification of Diseases, Ninth Revision (ICD-9) injury diagnosis admitted to 125 Oregon and Washington hospitals during 2001 and 2002 who survived to hospital discharge. The numbers of EMS transports and the total EMS costs were compared one year before and one year following the index hospitalization. RESULTS: There were 30,655 injured elders in our cohort. Their median ICD-9-based injury severity score was 0.97, with 4.1% meeting a definition of serious injury and 37% having hip fractures. The mean (range) numbers of EMS transports before and after the injury were 0.5 (0-45) and 0.9 (0-56), for an unadjusted incidence rate ratio (IRR) of 1.7 (95% confidence interval [CI] 1.7-1.8). The increase in EMS utilization following an injury hospitalization was even greater after adjusting for risk period and other model predictors (IRR 2.4, 95% CI 2.3-2.5). Annual mean EMS costs rose 74% following the injury hospitalization, from $211 to $367 per person. The greatest increase was in nonemergent EMS use, accounting for 67% of the increase in the number of uses. Institutionalization in a skilled nursing or rehabilitation facility either before or after injury was strongly associated with the need for EMS care. CONCLUSION: An injury hospitalization in the elderly serves as a sentinel marker for an abrupt increase in EMS utilization and costs, even after accounting for confounders.