Galectin-1 (Gal1) is a member of a highly conserved family of carbohydrate-binding proteins. It modulates innate and adaptive immune responses and fosters tumor-immune escape. Hodgkin lymphoma (HL) Reed-Sternberg cells overexpress and secrete Gal1, which selectively kills T helper (Th)1 and Th17 cells and cytotoxic T cells and promotes the immunosuppressive Th2/regulatory T-cell-predominant HL microenvironment. We developed a sandwich enzyme-linked immunosorbent assay and assessed serum Gal1 levels in 293 newly diagnosed, previously untreated patients with classical HL (cHL) enrolled in 3 risk-adapted clinical trials. Serum Gal1 levels were significantly higher in patients with cHL than in normal controls (P < .0001). Gal1 serum levels also increased with Ann Arbor stage (P = .012), areas of nodal involvement (P < .0001), and the International Prognostic Score (2-7, P = .019). We conclude that Gal1 serum levels are significantly associated with tumor burden and related clinical features in newly diagnosed cHL patients.