Metabolic syndrome (Mets) is a combination of disorders including abdominal obesity, impaired glucose tolerance, dyslipidemia and hypertension, which increases risk for cardiovascular disease (CVD) and type 2 diabetes when occurring together. In Japan, diagnosis criteria of Mets consists of an increased waist circumference and 2 or more of CVD risk factors. Annual health checkups and health guidance using Mets criteria were established in 2008 for the prevention of life-style related diseases in Japan. In this issue, history and diagnostic criteria of Mets and concerns for Mets concept were described.