Context: UV radiation is responsible for vitamin D synthesis and skin tanning. Longitudinal data relating skin color to vitamin D status are lacking. Objective: Our objective was to determine whether seasonal facial skin color changes are related to changes in 25-hydroxyvitamin D [25(OH)D]. Design and Setting: We conducted a prospective observational cohort study (Aberdeen Nutrition Sunlight and Vitamin D) with five visits over 15 months, starting spring 2006 with an additional visit in spring 2008 at a university medical research center in Scotland, 57° N. Participants: Participants included 314 Caucasian postmenopausal women, age 60–65 yr. Main Outcome Measures: Facial skin color was assessed by skin reflectance and expressed as the individual typology angle (ITA) (higher number indicates paler skin). 25(OH)D was measured by immunoassay. Results: Most women (43%) reported Fitzpatrick skin type III (always burns, always tans), 32% type II, and 25% type I (always burns, never tans). Overall, mean (sd) ITA in degrees were 36.6 (7.7), 38.2 (6.5), and 42.8 (5.3), respectively, for summer, autumn, and winter (P < 0.001). Linear regression showed that a 5° summer-winter change in ITA, was associated with a 15 nmol/liter change in 25(OH)D (P < 0.001) but did not predict winter 25(OH)D. Reported sunscreen use was associated with higher 25(OH)D. Mean (sd) 25(OH)D (nanomoles per liter) but not skin color was lower for the top body mass index quartile (Q4) compared with the other quartiles (summer: Q1, 57.1(19.9); Q4, 49.7 (20.4); P = 0.010) . Conclusions: Skin color change between summer and winter predicts seasonal 25(OH)D change. Low vitamin D status in obese women was not due to reduced sun exposure, suggesting that increased requirements or inaccessibility of vitamin D stores may be responsible.