In 2007, a patient safety programme was started to reduce hospital mortality in the Netherlands. The hospital standardized mortality ratio (HSMR) seems to be a promising indicator for monitoring the reduction of hospital mortality within hospitals. It is questionable, however, whether the HSMR can be used to compare the performance of hospitals. It has been shown that certain specialized procedures such as percutaneous transluminal coronary angioplasty (PTCA) and open heart surgery have an impact on the HSMR. Although this hampers a fair comparison between cardiac centres and general hospitals, the HSMR may still indicate whether a cardiac centre could improve its performance. Moreover, the impact of cardiac procedures on the HSMR is relatively modest, which shows that it is a robust indicator to monitor the intended decrease of hospital mortality on a national scale.