Muratov S, Lee J, Holbrook A, et al. - A retrospective, population-based comparative cohort study using administrative healthcare records was carried out in order to explain healthcare use and spending prior to and on becoming a new (incident) senior high-cost user (HCU) in comparison with senior non-HCUs, to evaluate the incremental costs, overall and by service category, attributable to HCU status, and to quantify its monetary influence on the provincial healthcare budget in Ontario, Canada. Costs attributable to incident senior HCU (n = 175,847) status estimated for nearly 1/10 of the provincial healthcare budget. A major contribution to the total incremental costs was made by prolonged hospitalizations. Furthermore, a subgroup of individuals that became HCU without hospitalization needs more investigation.