Regardless of which parts of the world they live in, most children will develop and grow at a similar rate if proper nutrition is ensured. Children from developing countries are at risk for primary malnutrition. Children undergoing anticancer therapy are at higher risk for secondary malnutrition, including obesity and growth retardation. Periodic nutritional assessments are important for planning effective dietary interventions for such children. In this review, we describe malnutrition as it occurs in children with cancer and various ways of assessing the nutritional status of these children, depending on the availability of resources in their local hospitals. Objective and subjective data should be used to complete the nutritional assessment. We discuss screening methods, including the use of subjective global assessment. Different parts of nutritional assessment include medical history; physical examination; biochemical and hematological data, such as visceral proteins, blood glucose levels, and lipid profiles, hemoglobin and hematocrit, and the lymphocyte count; anthropometric measurements; and food and nutrition history. We review medical tests and procedures to determine nutritional status, including nitrogen balance, delayed cutaneous hypersensitivity, prognostic nutritional index, creatinine height index, maldigestion and malabsorption tests, indirect calorimetry, and dual energy X ray absorptiometry (DXA scan). Evaluation and interpretation of data and estimation of nutritional risk are discussed, including proper techniques and use of anthropometric measures, selection and use of growth charts, calculation of caloric and protein needs, and the percentage of calories ingested. These methods will enable local health care providers to accurately assess the nutritional status of children with cancer, identify children at risk, and plan adequate nutritional interventions.