Background. Vitamin D deficiency in noncancer patients is associated with symptoms of fatigue, muscle weakness, and depression. These symptoms are common among advanced cancer patients. We investigated the prevalence of low serum vitamin D levels in cancer patients with fatigue or poor appetite and their association with symptom burden and other correctable endocrine abnormalities.Methods. This was a retrospective review of 100 consecutive cancer patients with appetite or fatigue scores of >4 of 10 referred to a supportive care clinic. We investigated serum levels of 25(OH) vitamin D, cortisol, thyroid-stimulating hormone, and bioavailable testosterone. Symptoms were measured by the Edmonton Symptom Assessment Scale. Serum 25(OH) vitamin D <20 ng/mL was considered deficient; >20 ng/mL and <30 ng/mL were considered insufficient.Results. Patients were predominantly male (68%) and