Measuring health system performance is essential for improving health and quality of care. It is relevant in any context, but especially in countries whose health care systems have undergone major changes. The 1989 transition from communism to democracy in Czechoslovakia followed by the 1993 split into two independent countries (the Czech Republic and Slovakia) have been studied extensively but little research has addressed the effects of these events on health and the quality of care provided. The overarching objective of this thesis is to examine pre- and post-transition health system performance at three levels: i) overall health and well-being, ii) quality of the health care system, and iii) quality of outpatient care. This is a policy piece intended to demonstrate the usefulness of various performance indicators, while applying a range of quantitative methods from different disciplines to unique datasets. The macro level findings suggest that the transition was not detrimental to overall health and wellbeing in neither of the two countries as demonstrated by a small continued height increase. Slovakia showed a larger capacity to benefit from the transition. The overall quality of the health care systems is measured by ‘avoidable’ mortality and also shows improvements. For some ‘avoidable’ mortality conditions Slovakia continues to lag behind the Czech Republic, while for others it outperforms its neighbour. The thesis also provides evidence on the absence of a significant relationship between health care inputs and ‘avoidable’ mortality. Finally, the assessment of the quality of outpatient care in Slovakia, using preventable hospitalisations and selected processes of care, shows that inappropriate care may be provided for asthma and diabetes. The findings also indicate a link between appropriate and inappropriate care and preventable hospitalisations. Overall, the results of this thesis provide the basis for policy makers to better understand the changes in health outcomes and quality of care in these two settings but also to inform future quality improvement efforts.