Objectives: Fibroblast growth factors (FGFs) represent potent effectors and play essential roles in both normal development and many pathological processes. Little is known about their possible implication in retinoblastoma growth. We sought to examine FGF high-and lowaffinity receptor (FGFR) expression, activation of FGFR1 by acidic FGF (FGF-1), and proliferative effects on Y79 cells. Methods: Expression of FGFR1 to FGFR4 was screened in Y79 cells by means of immunochemical and reverse transcriptase polymerase chain reaction techniques. Tyrosine phosphorylation of FGFR1 induced by FGF was examined by immunoprecipitation after stimulation with FGF-1 in the presence or absence of heparin. Retinoblastoma proliferation was monitored by radiolabeled thymidine incorporation or a vital dye-based assay, after addition of FGF-1 with or without inclusion of a specific FGFR1 neutralizing antibody or FGFR1 antisense oligonucleotides. Low-affinity heparan sulfate proteoglycan coreceptors were blocked through sodium chlorate or heparinase treatment of Y79 cells. Results: Y79 retinoblastoma expressed all 4 FGFRs, at both the protein and messenger RNA levels. The FGFR1 was differentially phosphorylated in a time-and heparindependent manner by FGF-1. Proliferation of Y79 cells induced by FGF-1 was entirely mediated by FGFR1, since inclusion of specific neutralizing antibodies or antisense oligonucleotides completely prevented tumor cell multiplication. Finally, FGF-1-induced proliferation was dependent on the presence and sulfation of heparan sulfate proteoglycan. Conclusions: Y79 retinoblastoma expresses all 4 FGFRs, but FGFR1 activation entirely accounts for FGF-1-driven cell proliferation. Clinical Relevance: These studies demonstrate a role for the FGF-1/FGFR1 pathway in retinoblastoma proliferation, and may contribute to developing therapeutic strategies to limit retinoblastoma growth.