A p53 yeast functional assay, which cannot only detect p53 gene mutations but also can assess p53 gene function, was used to screen for p53 gene dysfunction in human esophageal squamous cell carcinomas. Surgically resected frozen tissues of esophageal squamous cell carcinomas from 57 patients were examined for p53 gene mutation. Because the mean age of the patients diagnosed with esophageal squamous cell carcinoma was 64 years, we classified those who were <65 years of age as the Young Group and classified the others as the Elderly Group. The incidence of p53 gene mutations was 43 of 57 (75%). The incidence of p53 gene mutations observed in the Young Group was significantly higher than in the Elderly Group (P = 0.0007). Alcohol and smoking status did not relate to p53 gene mutation expression. Survival rate after surgery was not significantly associated with the presence of p53 gene mutation. However, in the Young Group with p53 gene mutation, those who had null mutations had a significantly shorter survival than those without null mutations (P = 0.0455). No other clinicopathological factors were associated with p53 gene mutations. Possibly, there may be a difference in esophageal carcinogenesis between the Young and the Elderly groups, because the incidence of p53 gene mutations is different between the two groups. In the Young Group, p53 gene mutation may cause esophageal carcinogenesis, and null mutation for p53 gene is a significant prognostic factor.