Vitamin D (vit D) insufficiency is highly prevalent in the nursing home population and associated with multiple negative outcomes, best documented in fractures and falls. Vit D supplementation has become a marker of quality of care. This semi-observational study has been set up to evaluate the adherence to treatment guidelines for vit D supplementation in nursing homes, by analyzing supplementation ratios (number of patients with vit D supplementation/total number of residents) over a period of 2years and after sensitization on 3 measurements in 17 voluntary, collaborating nursing homes, region Meetjesland, Belgium. The mean baseline supplementation ratio 24.3%, increased significantly to 56.7% by educating the responsible caregivers in nursing homes: coordinating general practitioners, directors, chief nurses. Moreover, a more appropriate dosage (i.e.≥800IU/d) was taken. This study demonstrates that it is possible to realize a significant improvement at little or no cost and with minimal efforts.