Abnormal amplification of epidermal growth factor receptor (EGFR) gene has been reported widely in various human tumors. However, the status of amplification of this gene in the process of carcinogenesis is not clearly defined. We used competitive polymerase chain reaction (PCR) to study whether EGFR gene is amplified and the degree of amplification in pre-malignant and malignant oral epithelial lesions, and also examined the relationship between EGFR gene aberration and the development of squamous cell carcinoma (SCC). Genomic DNA was extracted from paraffin sections of 17 cases of oral epithelial dysplasia (ED), four cases of carcinoma in situ (CIS), and 20 cases of untreated primary SCC. The extracted DNA was subjected to competitive PCR to amplify EGFR gene. Amplification of the EGFR gene was observed in three cases (17%) of ED, one case of CIS and four cases (20%) of SCC. In cases showing EGFR gene amplification, the degree of amplification was low in ED and CIS cases, whereas it was extremely high in SCC cases. These results suggest that amplification of EGFR gene occurs in the relatively early stage of the development of oral SCC. However, a high level of EGFR gene accumulation probably plays an important role in the progression to invasive cancer.