Study Objectives: Maintaining adequate serum levels of vitamin D may be important for sleep duration and quality; however, these associations are not well understood. We examined whether levels of serum 25(OH)D are associated with objective measures of sleep in older men. Setting and Participants: Cross-sectional study within a large cohort of community-dwelling older men, the MrOS study. Interventions: Among 3,048 men age 68 years or older, we measured total serum vitamin D. Objective estimates of nightly total sleep time, sleep efficiency, and wake time after sleep onset (WASO) were obtained using wrist actigraphy worn for an average of 5 consecutive 24-h periods. Results: 16.4% of this study population had low levels of vitamin D (< 20.3 ng/mL 25(OH)D). Lower serum vitamin D levels were associated with a higher odds of short (= 40.06 ng/mL) versus lowest (< 20.3 ng/mL) quartile of 25(OH)D, 2.15; 95 % confidence interval (CI), 1.21-3.79; P-trend = 0.004) as well as increased odds of actigraphy-measured sleep efficiency of less than 70% (OR, 1.45; 95% CI, 0.97-2.18; P-trend = 0.004), after controlling for age, clinic, season, comorbidities, body mass index, and physical and cognitive function. Lower vitamin D levels were also associated with increased WASO in age-adjusted, but not multivariable adjusted models Conclusions: Among older men, low levels of total serum 25(OH)D are associated with poorer sleep including short sleep duration and lower sleep efficiency. These findings, if confirmed by others, suggest a potential role for vitamin D in maintaining healthy sleep.