Using longitudinal medico-administrative data on hospital health costs and stays in Quebec between 1995 and 2012, we performed a decomposition of the variation in costs in order to analyze its main determinants. Over the period analyzed, the share of hospital stays accounted for 86% of the increase in hospital costs, compared to 14% for fee-for-service medical services. From 2008 to 2012, this distribution was 41% and 59%, respectively; the sharp rise in the cost of medical services has thus largely contributed to the rise in hospital costs. However, the increase in the volume of medical services contributed more than rate increases to total cost increase. Finally, we show that the effect of aging has little influence on the evolution of hospital health costs. It is more a combination of changes in disease prevalence and in practices that resulted in the overall increase in costs.