Improving performance in terms of delivery reliability is increasingly important for make-to-order (MTO) companies. Detecting improvement opportunities requires a structured diagnosis of the current performance. General problem-solving literature provides structures for diagnosis processes in general, but - depending on the performance problem to be diagnosed - a theoretical framework based on domain-specific scientific knowledge is required. This paper presents a framework for diagnosing delivery reliability performance in MTO companies. The framework consists of a diagnosis tree that structures the diagnosis process, enabling one to navigate from the achieved performance to the underlying causes related to production planning and control ...