Summary: A case formulation is the result of a complex process of interaction between assessing and assessed persons. There are many factors that exert their influence on this process and its result, although they are usually not even mentioned in the case formulation. This raises the question “What are the structure and characteristics of an adequate case formulation?”. Two different answers to this question are elaborated, both of which rely on an understanding of case formulations as structured sets of idiographic hypotheses, and are distinguished by different explications of the concept of idiographic hypothesis. The implications of the respective explications of the concept of idiographic hypothesis for the concept of case formulation are discussed. Finally, the question “If case formulations are construed as structured sets of idiographic hypotheses, how is the term 'structured set' to be understood?” is briefly addressed.