Galectins are evolutionarily conserved beta-galactoside-binding lectins which recognize specific glycoconjugates on the cell surface and the extracellular matrix. Accumulating evidence indicates that these proteins are involved in a variety of physiological and pathological processes including tumor growth and metastasis. Up-regulated expression of galectin-1 is a hallmark of a variety of malignant tumors. Here, we examined the expression of galectin-1 in glioma cell lines, the influence of ionizing irradiation and the intracellular and extracellular effects of this protein on tumor cell proliferation and migration. Galectin-1 was detected in both A172 and U118 glioma cells by immunoblot analysis. Ionizing irradiation induced a statistically significant up-regulation in glioma cell lines. RNA-interference-mediated silencing resulted in a significant suppression of the proliferation of the A172 cells, while the addition of recombinant galectin-1 had no effect. On the other hand, the migratory capacity of both cell lines was reduced after galectin-1 down-regulation, and up-regulated by the addition of exogenous galectin-1. Our results provide evidence of a role for galectin-1 in the regulation of glioma cell proliferation and migration. While an intracellular mechanism seemed to prevail in galectin-1-mediated regulation of tumor cell proliferation, the control of cell migration was exerted by both intracellular and extracellular mechanisms. In addition, this protein was up-regulated by ionizing radiation, indicating that the blockade of this protein should be performed before radiotherapy to avoid any undesired stimulating effects. Given the multifactorial role of galectin-1 in the regulation of tumor escape and metastasis, we conclude that targeting galectin-1 may have therapeutic benefits in the treatment of malignant glioma.