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 (HRs; with 95% confidence intervals) for all-cause and cardiovascular mortality in the first when compared with 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 HRs 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. © 2009 Blackwell Publishing Ltd.