By using data from the Survey of Health, Ageing and Retirement in Europe (SHARE), this article studies the within-country determinants of working pensioners and finds that demographic variables as well as health variables, economic variables and the pension system are important determinants why individuals choose to combine pension income with work income at the end of their working career. I apply counterfactual simulations to investigate cross-country variation. These counterfactual simulations reveal that variation in working pensioner proportions between countries can be explained by economic differences and differences in pension systems.