Low 25-hydroxyvitamin D (25(OH)D) and adiponectin levels are both associated with obesity and cardiovascular disease. Cross-sectional studies have suggested that 25(OH)D concentrations are positively associated with adiponectin, and that this relation may strengthen with increasing BMI. However, these studies had small samples sizes and did not account for many known confounders of adiponectin levels. We evaluated whether 25(OH)D was independently associated with circulating adiponectin in two large populations, and whether BMI modified this relationship. Cross-sectional analyses were performed on 1,206 women from the Nurses' Health Study I (NHS) and 439 men from the Health Professionals Follow-Up Study. Multivariable linear regression was used to analyze the independent association between 25(OH)D and adiponectin after controlling for potential confounders. Effect modification by BMI was examined by creating interaction terms between vitamin D and BMI. 25(OH)D concentrations were positively associated with circulating adiponectin in univariate analyses, and also independently associated with adiponectin after multivariable adjustments in both populations (women: β = 0.06, P < 0.001; men: β = 0.07, P < 0.05). BMI did not significantly modify the relation between 25(OH)D and adiponectin in either population. Higher 25(OH)D concentrations were independently associated with higher adiponectin concentrations in large populations of women and men. Since lower levels of 25(OH)D and adiponectin are associated with higher cardio-metabolic risk, assessing the effect of vitamin D supplementation on adiponectin levels is warranted.