We investigate the causal impact of retirement on health care utilization. Using SHARE data (from 2004 to 2013) for 10 European countries, we show that health care utilization increases when individuals retire. This is true both for the number of doctor's visits and for the intensity of medical care use (defined as the probability of going more than 4 times a year to the doctor's). This increase turns out to be driven by visits to general practitioners', while specialists' visits are not affected. We also find that the impact of retirement on health care utilization is significantly stronger for workers retiring from jobs characterized by long hours worked - more than 48 hours a week and/or being in the 5th quintile of the distribution of hours worked. This suggests that at least part of the increase in medical care use following retirement is due to the decrease in the opportunity cost of time faced by individuals when they retire.