Purpose of investigation: To determine the expression of matrix metalloproteinase-9 (MMP-9) expression in malignant and borderline ovarian tumors and its correlation to prognosis. Methods: Forty-five patients with primary epithelial ovarian tumors were enrolled in this retrospective study from 1988 to 2002. Only malignant (n = 30) and borderline (n = 15) ovarian tumors constituted the study group. All cases were surgically staged according to FIGO criteria. Patient characteristics and clinico-pathological findings were obtained from hospital records. Paraffin-embedded tissue blocks were treated with MMP-9 immunohistochemical stain. The percentage of the total number of tumors staining positively was categorised and awarded a score of 0 to 4: < 5% as 0, ≤ 6-25% as 1, 26-50% as 2, 51-75% as 3 and 76-100% as 4. The intensity of immunostaining was scored on a 3-point scale: 1, weak; 2, moderate and 3, intense. A weighed score for each tumor specimen was produced by multiplying the percentage score with the intensity score and was defined as the 'epithelial MMP-9 score'. Stromal staining was also assessed as weak, moderate and intense. Cases with final epithelial MMP-9 scores ≤ 6 and > 6 were then recategorised into two groups, accordingly. Based on degree of stromal staining, cases were recategorised into two final groups as mildly stained and intense or moderately stained. Tumor stages were regrouped as early (Stage I-II) and late (Stage III-IV), respectively. Results: Mean ages of cases with malignant and borderline ovarian tumors were 57.2 ± 3.1 and 49.7 ± 2.1 years, respectively. Epithelial MMP-9 scores were higher in malignant tumors compared to borderline tumors (p = 0.014). However, with regard to stromal MMP-9 staining, no significant difference was observed among malignant and borderline tumors (p = 0.113). Among malignant ovarian tumors, epithelial MMP-9 scores did not differ between early versus late-staged and well versus poorly differentiated tumors. Median survival time of cases with epithelial MMP-9 scores ≤ 6 and > 6 were 24 months and 32 months, respectively (log-rank: 0.93, p = 0.335). Cases with weak stromal MMP-9 staining had a longer median survival (48 months) compared to cases with moderate or intense stromal MMP-9 staining (24 months, log-rank: 4.46, p = 0.03). Conclusion: Epithelial MMP-9 expression generally appears in the malignant form of ovarian tumors compared to borderline tumors. MMP-9 expression in the stroma but not in the epithelium contributes to poor survival in ovarian cancers.