BACKGROUND: Low vitamin D status may be pronounced in Arctic populations due to limited sun exposure and decreasing intake of traditional food. OBJECTIVE: To investigate serum 25(OH)D3 as a measure of vitamin D status among adult Inuit in Greenland, predictors of low serum 25(OH)D3 concentrations and the trend from 1987 to 2005-2010. DESIGN: A total of 2877 randomly selected Inuit (≥18 years) from the Inuit Health in Transition study were included. A sub-sample (n = 330) donated a blood sample in 1987 which allowed assessment of time trends in vitamin D status. RESULTS: The geometric mean serum 25(OH)D3 (25[OH]D2 concentrations were negligible and not reported) in 2005-2010 was lowest among the 18-29 year old individuals (30.7 nmol/L; 95% CI: 29.7; 31.7) and increased with age. In all age-groups it decreased from 1987 to 2005-2010 (32%-58%). Low 25(OH)D3 concentrations (<50 nmol/L) were present in 77% of the 18-29 year old and decreased with age. A characteristic seasonal variation in 25(OH)D3 concentrations was observed (range 33.2-57.1 nmol/L, p<0.001), with the highest concentrations in August to October. Age (2.0% per year increase; CI: 1.7, 2.2), female gender (7.1%; CI: 2.0; 12.5), alcohol intake (0.2% per increase in drinks/week; 0.0; 0.4), and traditional diet (10.0% per 100 g/d increase; CI: 7.9; 12.1) were associated with increased serum 25(OH)D3, whereas smoking (-11.6%; CI: -16.2; -6.9), BMI (-0.6%; CI: -1.1; -0.2) and latitude (-0.7% per degree increase; CI: -1.3; -0.2) were associated with decreased concentrations. CONCLUSION: We identified a remarkable decrease in vitamin D status from 1987 to 2005-2010 and a presently low vitamin D status among Inuit in Greenland. A change away from a traditional diet may well explain the observed decline. The study argues for the need of increased dietary intake of vitamin D and supplementation might be considered.