In adults, prolonged deficiency of vitamin D (calciferol) can lead to osteomalacia, while lesser deficiency (insufficiency) is associated with various non-specific symptoms. Both vitamin D deficiency and insufficiency are becoming more common in developed countries. In the UK, the prevalence of vitamin D deficiency in all adults is around 14.5%, and may be more than 30% in those over 65 years old and as high as 94% in otherwise healthy south Asian adults. By comparison, the prevalence of vitamin D insufficiency in adults may be as high as 55%, and the condition is even more common in patients with osteoporotic fractures. Recently, we discussed the management of children with primary vitamin D deficiency. Here we review the management of adults with the condition.