Selenium (Se) is a trace element contributing to the structure of antioxidant system that saves cells from reactive oxygen species. Low serum Se levels have been reported in pediatric and adult patients with cancers. On the other hand, hair Se levels, predicting the long-term body Se status, have been reported in only adult patients with cancer. The aim of the study was to investigate the hair Se status in children with newly diagnosed lymphoid malignancies and the relation between malnutrition and Se deficiency. Thirty patients with leukemia (n = 17) and lymphoma (n = 13), and 25 healthy controls were enrolled to the study. Se was determined with atomic absorption spectrophotometrical method. Hair Se levels of the patients were significantly lower than those of control group [666.96 +/- 341.46 ng/g vs. 1019.22 +/- 371.83 ng/g (P<0.001)]. Children with lymphoma had lower Se than the children with acute lymphoblastic leukemia but not statistically significant [547.03 +/- 283.67 ng/g vs. 758.67 +/- 361.05 ng/g (P > 0.05)]. Malnourished patients (11/30) had lower hair Se levels (483.51 +/- 235.55 ng/g) than those of the controls (P = 0.036), whereas the Se levels of the patients who had no malnutrition (773.17 +/- 352.92 ng/g) were also lower than those of the controls but not statistically significant (P = 0.053). There was no correlation between age, sex, and the hair Se levels. In this study, we found that hair Se levels of the children with leukemia and lymphoma, especially those of malnourished patients, were lower than those of controls. Additional studies are needed to determinate whether low levels of hair Se may play a role in carcinogenesis.