Vitamin D via its immunomodulatory properties has been reported in some studies to reduce cancer progression and improve survival from cancer. However, children with cancer are at a high risk for vitamin D deficiency due to treatment modalities, prolonged hospital admissions and poor nutrition from anorexia, mucositis and recurrent vomiting. Although, there is a high rate of vitamin D deficiency worldwide and a higher rate in developing countries, the burden of vitamin D in children with cancers in developing countries remains unknown. Hence the study aimed to assess the serum 25-hydroxyvitamin D level in children with cancer and compared same with apparently healthy controls. A secondary objective was to identify risk factors associated with vitamin D deficiency in children with cancer. The study was a comparative cross-sectional study conducted over a 9 month period from November 2017 to July 2018 on children aged 0-17 years with cancer at the Paediatric Haematology and Oncology ward at the Lagos University Teaching Hospital (LUTH) and 75 apparently healthy children who were age and sex matched as controls from various surgical and paediatric outpatient clinics of LUTH. Data on the type of cancer and treatment received was obtained from the participant’s case note while a questionnaire was administered for other information such as sun exposure and dietary intake. The serum 25-hydroxyvitamin D level of the study participants was measured using High Performance Liquid Chromatography (HPLC) and classified using the Global Consensus recommendations as vitamin D deficiency, insufficiency and sufficiency. Vitamin D deficiency was accordingly defined as serum 25- hydroxyvitamin D levels <30 nmol/L.