Basic fibroblast growth factor is one of a class of heparin-binding growth factors that stimulates endothelial cell proliferation and migration in vitro and angiogenesis in vivo. The purpose of this study was to investigate the expression of basic fibroblast growth factor in chronic periapical lesions of endodontic origin. Ten chronic inflammatory periapical lesions were examined using immunohistochemical staining. The experimental control group consisted of four specimens of uninflamed periodontal ligament tissue. Two independent observers graded the staining intensity for basic fibroblast growth factor. An immunopositive, cytoplasmic, and nuclear reaction for basic fibroblast growth factor, with varying degrees of upregulation was observed in all 10 chronic periapical lesions. We speculate that the formation of granulation tissue and the activation of epithelial cell rests in chronical apical lesions might be associated with a local rise in the tissue level of basic fibroblast growth factor. Therefore, this growth factor could play an important role in the pathogenesis of chronic apical periodontitis and periapical cysts.