Esophageal carcinoma is one of the most lethal tumors, and identification of prognostic factors for patients with this disease is important. Propyl isomerase Pin1 is overexpressed in some human cancers and thought to be an important regulator of cyclinD1. However, the relationships between Pin1 expression and clinicopathologic features in patients with esophageal squamous cell carcinoma (SCC) have not been explored. Here, we investigated the role of Pin1 in association with cyclinD1 in esophageal SCC progression and its clinicopathological significance. The expressions of Pin1 and cyclinD1 were examined immunohistochemically in surgical specimens from 119 esophageal SCC patients. The expression levels of Pin1 and cyclinD1 in 6 esophageal SCC-derived cell lines were compared with those in an immortalized human esophageal cell line by western blotting. Pin1 overexpression was correlated with lymph node metastasis (P=0.0384), and its expression was related to cyclinD1 expression. Pin1 expression was correlated with poor prognosis in esophageal SCC patients (P=0.0044), and found to be an independent prognostic factor (P=0.0277). Pin1 was overexpressed in 5 of 6 esophageal SCC-derived cell lines compared with immortalized esophageal keratinocytes. Moreover, the Pin1 level was correlated with the cyclinD1 level in 4 of the 6 cell lines. In conclusion, Pin1 expression is correlated with cyclinD1 expression and may be a useful prognostic factor for esophageal SCC.