The cyclin D1, referred to as PRAD-1, has been mapped to the 11q13 region, and its expression has been detected in squamous cell lines and several primary esophageal carcinomas. We assessed cyclin D1 amplification in 122 squamous cell carcinomas of the esophagus. Samples for DNA extraction were obtained from formalin-fixed paraffin-embedded specimens, and 10 microgram of each DNA sample were subjected to slot blot analysis. The presence of more than three gene copies was considered evidence of gene amplification. Amplification of cyclin D1 was detected in 28 (23%) of 122 cases of squamous cell carcinoma of the esophagus. There were no significant differences between the clinicopathological background factors in groups positive and negative for cyclin D1 amplification, but the survival rate of patients exhibiting amplification was significantly lower (P < 0.001). The groups were stratified according to the pN (pathological N category) factor and pT (pathological T category) factor in the TNM classification, and the cumulative survival rates in the amplification groups were always significantly lower. Amplification of cyclin D1 was correlated with distant organ metastasis after curative operations, but there was no significant difference in lymph node recurrence rates of patients with or without amplification. Cyclin D1 amplification had the second highest partial regression coefficient in the multivariate analysis, after the pN factor. Amplification of cyclin D1 was independent of the TNM classification as a prognostic factor, and was a useful marker for predicting outcome and distant organ metastasis in patients with squamous cell carcinoma of the esophagus. It appears that appropriate treatment can be selected by evaluating both TNM factors and cyclin D1 amplification.