A prospective longitudinal study was conducted to analyze the evolution of the nutritional status of 34 children (12 girls and 22 boys), aged 1.5-15.8 years (median age 9.06), undergoing autologous peripheral blood stem cell transplantation (PBSCT). The nutritional status was evaluated at baseline, days +1 and +7, discharge, and day +30 by dietary or parenteral intake, anthropometric and laboratory measurements, and nitrogen balance. At baseline, changes in anthropometric (53%) and biochemical measurements (83%) are frequent but mild. The mean caloric intake was normal. Children with normal values for the anthropometric parameters all had an intake > 80% (p < .01). No correlation was found between the anthropometric and biochemical parameters. During transplantation, significant changes (p < .001) were found for energy intake, albumin, transferrin, and nitrogen balance. Fibronectin, prealbumin, and retinol-binding protein showed only a few changes. All but prealbumin recovered on day +30. No correlation was found between the nutritional status and toxicity or infection in children undergoing autologus PBSCT. The changes in the nutritional status observed at the start of transplantation correlated with the nutrional intake. Anthropometric and biochemical changes are complementary. The results may be ascribable to the fact that the patients in this series had mild malnutrition.