Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases associated with tumor progression. It was proved that expression of MMP-9 in human esophageal cancer tissues correlated with stages of the disease. The aim of the present study was to determine potential clinical use of serum MMP-9 as a tumor marker of esophageal cancer.The study included 89 patients with esophageal cancer and 30 healthy subjects (control group). We assayed serum levels of MMP-9 and classical tumor markers (SCC-Ag and CEA). We defined the prognostic value and diagnostic criteria for the measurands.Serum levels of MMP-9, CEA and SCC-Ag in esophageal cancer (EC) patients were statistically higher than in the control group. MMP-9 serum concentrations were associated with clinical stages of EC and tumor size. The diagnostic sensitivity of MMP-9 (70%) was higher than tumor markers and increased in combination with SCC-Ag (92%). The area under the ROC curve for MMP-9 (0.733) was lower than for SCC-Ag (0.811) and higher than for CEA (0.673). In Cox's univariate analysis serum MMP-9, SCC-Ag and CEA were not significant for prognosis of EC.The results suggest the usefulness of MMP-9 as a tumor marker in diagnosis, but not in prognosis of esophageal cancer.