The authors have argued that complexity in general health care is increasingly prevalent because of the increase in patients who have multimorbid conditions, and the increased professional and technical possibilities of medicine. In the increasingly complex care systems, it is necessary-specifically when treating patients in need of integrated care by several providers-that an optimal match between case and care complexity be found in order to prevent poor outcomes in this vulnerable group. The authors discussed several approaches to case complexity that can be identified in the literature. Most of them seem unsuitable for adjusting case and care complexity, and inadequate for designing multidisciplinary care. Theoretic approaches to case complexity may be of interest, but did not result in clinically meaningful information. The INTERMED, which can be considered the first empirically based instrument to link case and care complexity, is an attempt to improve care delivery and outcomes for the complex medically ill.