Nutritional status in children is an indicator of health and well-being at both the individual and the population level. Screening for malnutrition should be an integral part of pediatric care universally. Nutritional intervention requires repeated measurement of nutritional status to assess severity and to track progress over time. Methodological issues in the assessment of nutritional status are reviewed with emphasis on anthropometric measurement, body composition, and energy expenditure of children at risk for malnutrition. Use of reference data, measurement error, maturational effects, and hereditary factors are among the issues reviewed and serve as guidelines in the interpretation of measurement of nutritional status.