The research presented in this paper has been done in the context of the further development of the methodology of calculating the Hospital Standardised Mortality Ratio (HSMR) in the Netherlands. It has been funded by Dutch Hospital Data (DHD). The goal of this research is to investigate the effect of adding post-discharge mortality to the HSMR. The advantage of adding post-discharge mortality, is that the mortality indicator becomes less dependent on the discharge policies of hospitals. Pouw et al. (2013) have investigated the possibilities and effects of adding post-discharge to the mortality indicator in the Netherlands. They concluded that this would lead to an improvement of the indicator. However, they did not investigate what the optimal period should be in which the post-discharge mortality is taken into account, whether or not the length of the period should differ between diagnosis groups and whether this period should be from admission or from discharge. These questions have been investigated by Statistics Netherlands and the results are presented in this paper (in Dutch).