Over the last century, chronic health problems have replaced infectious diseases as the dominant health care burden. Multimorbidity, the cooccurrence of multiple chronic diseases in the same person, has been defined as the “most common chronic condition,” and its prevalence progressively increases with age, affecting more than 60% of people aged 65 or older. Multimorbidity has a relevant impact on patient’s outcomes and health care costs in both younger and older adults. Compared to those with single conditions, patients with multimorbidity are more likely to die prematurely, be admitted to hospital, have poorer quality of life, and receive polypharmacy.

Despite the increasing interest of the researchers in this field, there is still a remarkable gap between the harmful impact of multimorbidity at the individual and societal level and the amount of scientific and clinical research devoted to this topic. Current knowledge on multimorbidity can be summarized as follows: (1) multimorbidity affects more than half of older persons; (2) the prevalence increases with age, in women, and in people from lower social classes; (3) very little is known about risk factors for multimorbidity, genetic background, biological causes (such as cholesterol, blood pressure, or obesity level), life styles (such as smoking, drinking, nutrition, or physical activity), environmental factors (air pollution and social environment), or the effect of new diseases by itself; (4) functional impairment, poor quality of life, and high health care utilization and costs are major consequences of multimorbidity; and (5) data are insufficient and not integrated to provide scientific basis for evidence-based care of patients affected by multimorbidity.

Patients with multimorbidity have the most complex health needs but, due to the current disease-oriented approach in healthcare, they face a highly fragmented care that leads to incomplete, inefficient, ineffective, and even potentially harmful interventions. Complexity of care in patients with multimorbidity requires the involvement of a large number of healthcare providers and resources. While there are examples of integrated care programs for chronic diseases implemented in relatively small populations, there are no widely accepted care models for multimorbidity.

We invite investigators to contribute original research articles as well as review articles that seek to address epidemiology of multimorbidity both in the general population and in clinical settings. A particular interest will be given to papers exploring causes of multimorbidity and exploring the prevalence, type, and impact of the presence of multiple cooccurring diseases in important chronic index diseases. Evidence about different models of care for persons with multimorbidity will also be welcomed.

Potential topics include, but are not limited to:

• Basic research articles especially covering modelling of multimorbidities
• Genetics and genomics in multimorbidity
• Development of multimorbidity in disease-free populations
• Common risk factors for multimorbidity
• Clustering of chronic diseases
• Models of care for persons affected by multimorbidity in different settings, especially in primary care
• Health care utilization and medical costs
• Ethical aspects of multimorbidity treatment
• Design of future studies on multimorbidity and its main outcomes