COPD, once thought only to be a disease of the lungs, is now established as a common complex multisystem disease with multiple comorbidities that contribute to symptoms, exacerbations, hospital admissions and mortality. The most notable of these comorbidities include cardiac and cerebrovascular disease, diabetes, hypertension, asthma, pneumonia and depression. Estimation of the prevalence of COPD, as well as its comorbidities, is difficult because of the variability in definitions and methods used. However, recent large epidemiological studies have helped us to understand better the prevalence and effects of COPD comorbidities. The pathogenesis behind many of these comorbidities remains a focus of active investigation. Successful management of COPD comorbidities is central to improving overall outcomes in COPD. © ERS 2013.