The aetiology of CVD is still not completely understood. The present review article summarises data supporting the hypothesis that an insufficient vitamin D status may contribute to the worldwide high prevalence of CVD. Human vitamin D status primarily depends on skin exposure to the UVB spectrum of the sunlight. Epidemiological data indicate that geographic latitude, altitude, season, and the place of residence (urban or rural) are associated with CVD mortality. Interestingly, all these factors also have an influence on human UVB exposure and thus on vitamin D status. Several mechanisms might be responsible for a protective role of vitamin D in CVD. These mechanisms include the inhibition of vascular smooth muscle proliferation, the suppression of vascular calcification, the down regulation of pro-inflammatory cytokines, the up regulation of anti-inflammatory cytokines, and the action of vitamin D as a negative endocrine regulator of the renin-angiotensin system. The first intervention trials indicate that vitamin D may suppress cardiovascular risk markers. However, more controlled clinical trials are needed to investigate whether optimal oral vitamin D supplementation is able to reduce CVD morbidity and mortality.