Background: People with intellectual disability (ID) are thought to be at an increased risk of fractures. The extent of this increase in risk has been incompletely documented in the literature, and the underlying reasons remain to be elucidated. Methods: The aims of our study were to document the vitamin D status and fracture incidence in an intellectually disabled population, to test for associations between vitamin D status and possible risk factors for reduced vitamin D levels, and to determine the efficacy of oral vitamin D supplementation in restoring appropriate vitamin D levels in those found to be vitamin D insufficient. A 5-year retrospective audit of fractures in 337 individuals with ID receiving health care at a residential facility was performed. Data analysed included age, gender, mobility, dietary status, incident fractures, medications and 25-hydroxyvitamin D levels. Vitamin D insufficient individuals received oral vitamin D supplementation, and had repeat testing to assess treatment efficacy. Results: In total, 57 of individuals tested were found to be vitamin D insufficient. Vitamin D insufficiency was strongly correlated with reduced mobility P less than 0.001 (P<0.001) and difficulty with consuming solids P less than 0.001 (P<0.001). However, the correlation between vitamin D levels and fractures was not significant (P= 0.3). Oral vitamin D supplementation using cholecalciferol (vitamin D3) 100 000 International Units (IU) every 4 months was effective in correcting vitamin D insufficiency. Sixty-eight fractures occurred over the study period in 52 individuals, a rate of 1 fracture every 23.8 person years. A total of 55 of these fractures involved the extremities. Fractures were more common in men than in women. Peripheral fractures (hand, foot, wrist, ankle) accounted for 54 of all fractures, and were particularly prevalent in the most mobile individuals. Conclusions: Fractures and vitamin D insufficiency are relatively common in people with ID. This study did not find a significant association between vitamin D insufficiency and fractures in the study population. Oral vitamin D supplementation is effective in restoring normal vitamin D levels, and should be considered routinely for those at the highest risk. [Author abstract altered to comply with ERIC guidelines.]