SUMMARY Objective: Vitamin D deficiency is common among the elderly and may contribute to cardiovascular disease. The aim of our study was to elucidate whether low serum levels of 25-hydroxyvitamin D [25(OH)D] are associated with an increased risk of all-cause and cardiovascular mortality. Design and patients: The Hoorn Study is a prospective population-based study among older men and women. Measurements: Fasting serum 25(OH)D was determined in 614 study participants at the follow-up visit in 2000-2001, the baseline for the present analysis. To account for sex differences and seasonal variations of 25(OH)D levels we formed sex-specific quartiles, which were calculated from the 25(OH)D values of each season. Results: After a mean follow-up period of 6.2 years, 51 study participants died including 20 deaths due to cardiovascular causes. Unadjusted Cox proportional hazard ratios (with 95% confidence intervals) for all-cause and cardiovascular mortality in the first when compared to the upper three 25(OH)D quartiles were 2.24 (1.28-3.92; p=0.005) and 4.78 (1.95-11.69; p=0.001), respectively. After adjustment for age, sex, diabetes mellitus, smoking status, arterial hypertension, high density lipoprotein cholesterol, glomerular filtration rate and waist to hip ratio, the hazard ratios remained significant for all-cause [1.97 (1.08-3.58; p=0.027)] and for cardiovascular mortality [5.38 (2.02-14.34; p=0.001)]. Conclusions: Low 25(OH)D levels are associated with all-cause mortality and even more pronounced with cardiovascular mortality but it remains unclear whether vitamin D deficiency is a cause or a consequence of a poor health status. Therefore, intervention studies are warranted to evaluate whether vitamin D supplementation reduces mortality and cardiovascular diseases.