The health care sector is a huge industry in many Western countries going through fundamental changes, with increasing needs for new monitoring systems and performance indicators. The aim of this paper is to identify factors that influence the success of external reporting systems, which will ultimately affect the transparency and performance of the sector. We review theory on performance indicators, national care systems, and inter-organizational reporting systems, resulting in formulating several hypotheses. We use a data set and 12 interviews in one case study (the mental health care sector in the Netherlands) to evaluate the hypotheses. Our findings show that the new system is more successful for integrated care organizations than specialized care organizations, and more successful if care organizations have better internal information systems.