Metabolic syndrome is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. It affects a large number of people, and prevalence increases with age. Some studies estimate the prevalence in the USA to be up to 25% of the population.

Metabolic syndrome is also known as metabolic syndrome X, syndrome X, insulin resistance syndrome, Reaven's syndrome or CHAOS (Australia). A similar condition in overweight horses is referred to as equine metabolic syndrome; it is unknown if they have the same etiology.