Epithelial growth factor receptor (EGFR) sends signals to the proliferation signal transduction system, receiving two ligands: epithelial growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). This immunohistochemical study examined the roles of EGFR and its ligands in the proliferation of normal and neoplastic vulvar squamous cells in 25 patients with vulvar squamous cell carcinoma (VSCC), 10 patients with vulvar condyloma acuminata (VCA), 15 patients with vulvar intra-epithelial neoplasm I-II or III (VIN I-II or III), and 5 subjects with vulvar normal squamous cells (VNSC). EGFR was detected in a few basal cells in 40% of the VNSC, in highly dysplastic cells in 40% of the VIN III, in many neoplastic cells in 80% of the VCA, and in some malignant cells in 64% of the VSCC. EGF was seen in the cytoplasm in 20% of the VIN I-II, 100% of the VIN III, 100% of the VCA, and 100% of the VSCC. Diffuse TGF-alpha was weakly expressed in the cytoplasm in 100% of the VNSC, more intensely in 100% of the VIN and 100% of the VCA, and intensely in 100% of the VSCC. These findings led to the suggestion that the TGF-alpha-EGFR system maintains the growth of normal squamous cells and, in part, maintains the growth of dysplastic and neoplastic squamous cells in the vulva. EGF expression was an early sign of neoplasia. The expression of EGFR with overexpression of its two ligands contributed to the proliferation of dysplastic and neoplastic squamous cells in VIN III and VCA. EGFR expression appeared to contribute to essential neoplastic abnormalities in 64% of the VSCC.