Vitamin D insufficiency has been found to be as high as 75% among community-dwelling adults aged 65 and older. The purpose of this article is to provide a review of published literature focused on the benefits of vitamin D and calcium supplementation in older patients with cancer. Insufficient vitamin D levels may have considerable effects on cancer-related diagnosis and treatment. Patient education should include information concerning vitamin D and calcium administration to reduce falls and injury from falls and enhance functional status. This article will consider the issue of vitamin D levels related to cancer prevention, diagnosis, treatment, functional status, and falls in older patients with cancer. Dosing and serum measurement information will be discussed.