Malnutrition in children with cancer is reported to be relatively uncommon at the time of diagnosis. However, in most studies nutritional status measurement has relied almost exclusively on weight-related indices. This can be misleading, because in children with malignancy, tumor masses can reach more than 10% of total body weight. A controlled study was performed in 62 patients using arm anthropometry to provide a more accurate evaluation of the nutritional status of children with cancer at presentation. Height, weight, midupper arm circumference (MUAC), and triceps skinfold thickness (TSFT) were measured in all patients (40 boys, 22 girls) and controls (18 boys, 13 girls). Weight for height (WFH) of each patient was compared with the national standards. MUAC and TSFT were also interpreted according to the standards developed by A. Roberto Frisancho. The mean ages were 6.5 +/- 3.7 years (range 0.08-13) and 5.7 +/- 4.7 years (range 0.25-15) in patients and control group, respectively. Results showed that although the WFH values for patients were normal, MUAC and TSFT values were significantly less than control values (P < 0.001). Moreover, 27% of patients showed malnutrition (they had MUAC and TSFT below 5th percentile). Patients with intraabdominal solid tumors had significantly lower MUAC and TSFT values than those with extraabdominal solid tumors (P < 0.05). The data strongly indicate that malnutrition is common at the time of diagnosis in children with cancer, and arm anthropometry should replace the use of weight-related indices to identify malnutrition in children.