This cross-sectional study examined the burden of cardiovascular diseases (CVDs) using serum 25-hydroxyvitamin D (25[OH]D) and prevalence of hypovitaminosis D in adults with CVDs using data from NHANES 2001 to 2004. Serum 25(OH)D levels were divided into 3 categories (≥30, 20 to 29, and <20 ng/ml), and hypovitaminosis D was defined as vitamin D <30 ng/ml. Of 8,351 adults who had 25(OH)D measured, mean 25(OH)D was 24.3 ng/ml, and the prevalence of hypovitaminosis D was 74%. The burden of CVDs increased with lower 25(OH)D categories, with 5.3%, 6.7%, and 7.3% coronary heart disease; 1.5%, 2.4%, and 3.2% heart failure; 2.5%, 2.0%, and 3.2% stroke; and 3.6%, 5.0%, and 7.7% peripheral arterial disease. Across all CVDs, hypovitaminosis D was more common in blacks than Hispanics or whites. Compared with persons at low risk for CVDs (68%), it was more prevalent in those at high risk (75%; odds ratio [OR] 1.32, 95% confidence interval [CI] 1.05 to 1.67), with coronary heart disease (77%; OR 1.48, 95% CI 1.14 to 1.91), and both coronary heart disease and heart failure (89%; OR 3.52, 95% CI 1.58 to 7.84) after controlling for age, race, and gender. In conclusion, hypovitaminosis D was highly prevalent in US adults with CVDs, particularly those with both coronary heart disease and heart failure.