Objective: Osteopontin (OPN) is a secreted integrin-binding glycophosphoprotein that may have a role in head and neck squamous cell carcinoma (SCC). To evaluate the clinical significance of OPN in esophageal squamous cell carcinoma (ESCC), we compared plasma OPN levels with those of common tumor markers. Methods: Preoperative plasma OPN levels were measured by enzyme immunoassay in 103 ESCC patients. Serum SCC antigen, Cyfra 21-1, and carcinoembryonic antigen (CEA) levels were also measured routinely at admission by radioimmunoassay. Results: Plasma OPN levels ranged from 82.8 to 1,980 ng/ml. High OPN level was associated with lymph node metastasis (p = 0.05), but not with tumor histology or depth of invasion. The overall survival of the patients with high OPN levels was worse than that of those with low OPN levels (p = 0.02). SCC antigen and Cyfra 21-1 levels were associated with the depth of tumor invasion, the tumor diameter, lymph node metastasis, and the overall survival, but CEA was not associated with these clinicopathological factors. Combined evaluation of OPN plus Cyfra 21-1 or OPN plus SCC antigen was useful as an independent prognostic indicator. Conclusion: Measurement of the plasma OPN level, as well as serum SCC antigen and Cyfra 21-1, may help to predict the progression of ESCC.