Mild and marginal malnutrition must be identified to prevent the development of severe protein-energy malnutrition in pediatric cancer patients. We aimed to evaluate nutritional status and determine daily energy, protein and micronutrient intake to identify mild or marginal malnutrition in pediatric cancer patients. Daily energy, protein and micronutrient intake, anthropometric measurements and biochemical indices were studied in 45 patients (25 in remission, 20 newly diagnosed or relapsed) who consumed energy, protein, vitamins and minerals below the recommended quantities. According to the weight-for-height index, 23 children (51.1%) were determined to be malnourished. Absolute and relative prealbumin values were 19.4 +/- 7.2 mg/dl and 74.3 +/- 29.1 mg/dl in the remission group, and 14.8 +/- 5.1 mg/dl and 58.1 +/- 23.3 in the active disease group, respectively (p < 0.05). Relative prealbumin values were found to be low in 63.6 percent of nonmalnourished children, and 80 percent of children with mild malnutrition. We conclude that malnutrition is common in pediatric cancer patients, and prealbumin is a reliable and sensitive indicator of mild and marginal malnutrition. Determining prealbumin values and assessing the deficiency of micro- and macronutrients before malnutrition is detected by anthropometric measures may provide a warming that nutritional problems may occur.