Galectin-1, a member of the beta-galactoside-binding galectin family, is a pleiotropic dimeric protein participating in a variety of normal and pathological processes, including cancer progression. Modulation of the interactions with the basement membrane glycoprotein laminin and induction of apoptosis in activated T lymphocytes are well-known functions of this galectin. In this study, the expression of galectin-1 was examined in 148 human primary prostate carcinoma samples. Immunohistochemical staining of paraffin sections of prostate tissues revealed that galectin-1 was not detected in normal, PIN (prostatic intraepithelial neoplasia) or carcinoma cells, but accumulated in the stroma and associated fibroblasts. Galectin-1 expression was significantly increased in the tumour-associated stroma compared with the non-neoplastic gland-associated stroma in 21.3% of the cases (Mantel-Haenszel test, p=0.001; Wilcoxon signed rank test, p<0.0001). Increased galectin-1 expression in the cancer-associated stroma compared to the normal gland-associated stroma (p=0.03) was identified by multivariate analysis as a strong independent predictor of prostate-specific antigen (PSA) recurrence, just after the pathological stage (p<0.0001). The association between accumulation of galectin-1 in the stroma of the malignant tissue and aggressiveness of the tumour adds weight to the body of evidence that identifies a role for galectin-1 in the acquisition of the invasive phenotype. In addition to modulating cancer cell interactions with laminin, galectin-1 accumulated around the cancer cells may act as an immunological shield by inducing activated T-cell apoptosis. This exciting hypothesis warrants further investigation.