The westernised world is in the midst of an epidemic of type 2 diabetes and associated cardiovascular disease. These closely interlinked conditions have a common pathophysiological basis underpinned by insulin resistance and the metabolic syndrome. Contemporary changes in environmental factors on a background of genetic susceptibility are thought to account for the increases seen. Life on earth is governed by the 24-hour environment of light and darkness cycling with the rotation of the earth. Numerous metabolic and physiological pathways are coordinated to this 24-hour cycle by an endogenous clock. Recent epidemiological evidence and animal data suggest that disturbance of circadian rhythms through genetic and environmental influences on the molecular clock is pivotal in the pathogenesis of obesity, type 2 diabetes and cardiovascular disease. This review describes current knowledge on the topic.