As a new member of the CD4(+) effector T-cell family, T-helper 17 (Th17) cells, have emerged as an important mediator in inflammatory and autoimmune diseases. Th17 cells preferentially produce interleukin (IL)-17A, IL-17F, IL-21, IL-22, and IL-26 in humans. Recent studies suggest a potential role for Th17 cells in tumour development. The current study was designed to investigate the possible involvement of Th17 cells in the brain tumour medulloblastoma. Compared with 17 healthy volunteers, 23 patients with medulloblastoma had a higher proportion of Th17 cells in their peripheral blood. Increased populations of Th17 cells were also present in medulloblastoma-infiltrating T-cells. Furthermore, the mRNA levels for Th17-related factors (IL-17, IL-23 and retinoid orphan nuclear receptor) in tumour tissues and the serum concentrations of IL-17 and IL-23 protein were significantly increased in patients with medulloblastoma. The results indicate that Th17 cells may contribute to medulloblastoma pathogenesis.