[Multimorbidity is not a diagnosis].

We have been studying multimorbidity in epidemiology and clinical practice since the 1970s. Growing experience shows that the concept of multimorbidity is helpful for epidemiologists to describe population-level changes, but of little use to patients and clinicians who 'diagnose' multimorbidity. Several large, rigorous clinical trials show that organizational changes in primary care can improve the care of these complex patients, but do not improve directly health-related quality of life. This article describes the history of multimorbidity and results of recent randomized trials to prompt a discussion of new approaches to improve the experience of people living with multiple chronic diseases.