Objective: The possible extra-skeletal effects of vitamin D have attracted considerable interest. Suboptimal levels of vitamin D have been associated with higher risk of developing type 2 diabetes, and vitamin D has been thought to affect glucose homeostasis, but evidence is lacking. This paper aims to investigate whether intervention with vitamin D3 (cholecalciferol) will improve glycemic control in individuals with type 2 diabetes and vitamin D deficiency, and whether the effect differs with ethnicity. Materials and methods: As part of the DIVINE study at Oslo University Hospital, a randomized, controlled, double blinded trial, glycated hemoglobin (HbA1c) was measured in 62 subjects. 33 subjects (23 Nordic and 10 South Asian) were randomized to cholecalciferol 400 000 U, with additional 200 000 U if serum 25-hydroxyvitamin D < 100 nmol/L at 4 weeks. 29 subjects (20 Nordic and 9 South Asian) were given placebo. HbA1c was measured again after 6 months. Results: Intervention with vitamin D3 showed no significant effect on change in median [IQR] HbA1c from randomisation to end of study: vitamin D group 0,1 [0,9]% and placebo group 0,25 [0,6]%, p for difference in change = 0,812, and there was no significant difference in change in median HbA1c between the Nordic and the South Asian group, p-value 0,643. Discussion: Treatment with vitamin D showed no effect on HbA1c in individuals with type 2 diabetes and vitamin D deficiency, neither in total, nor when divided into ethnic subgroups. The results should, however, be interpreted with care due to small sample size.