The nm23 gene is a reported metastasis suppressor gene. Recent studies have shown that its expression has tissue specificity. The role of nm23 in human ovarian cancer is still controversial. This study examines the prognostic significance of nm23 expression in patients with serous ovarian carcinoma. Following comparative proteomics in 13 fresh frozen ovarian serous cancer tissues with other histological types of ovarian cancers, validation was performed using immunohistochemistry on clinically well-designed 73 ovarian serous carcinoma microarray samples that were retrieved from ovarian cancer patients from 1990 to 2003. Statistical analysis of the results was performed using chi(2) test, Cox proportional regression, the Kaplan-Meier method and log-rank test. We found that the expression of nm23 inversely correlated with peritoneal seeding (P=0.009). However, strong nm23 expression was associated with mortality in patients with ovarian carcinoma in univariate analysis (P=0.04). Poor prognostic factors of disease-free survival included tumor residue more than 2 cm (P=0.02), bilaterality (P=0.01) and peritoneal seeding (P<0.01), whereas poor prognostic factors affecting overall survival included peritoneal seeding (P=0.05). In Kaplan-Meier analysis, strong nm23 immunoreactivity correlates with poor overall survival (P=0.04) but not with poor disease-free survival. In conclusion, overexpression of nm23 is independently associated with decreased overall survival in patients with ovarian carcinoma and also significantly correlates with mortality. Nm23 may have a biological function that leads to poor clinical outcomes in ovarian carcinoma.