This paper is intended to further the understanding of the role of the characteristics of decision making and its environment in the development of sustainable partnerships in health care, and to illustrate how this subject can be studied from a combined theoretical and methodological perspective. With the aid of a conceptual model covering sensitizing concepts from contingency theory (that refer to environmental characteristics--particularly institutions--the process course of decision making and its outcomes) and the case study methodology (explanation-building, triangulation, document study and interviews), two Dutch cases were analysed. The findings indicate which environmental characteristics are responsible for the differences in the process course and outcomes between the cases.