The aim of this study was to determine the immunohistochemical distribution of survivin in benign, borderline, and malignant serous tumors of the ovary. Survivin was localized by an indirect immunoperoxidase method in 42 cases of serous tumors of the ovary (15 cystadenomas, 15 borderline tumors, and 12 cystadenocarcinomas). Nuclear staining and cytoplasmic staining were separately scored. Cytoplasmic staining was detected in 27% of adenomas/borderline tumors and in 58% of carcinomas. Nuclear staining was detected in 87% of adenomas/borderline tumors but in only 42% of carcinomas. Although the differences in the intensity of cytoplasmic staining between adenomas and borderline tumors versus carcinomas were not significant, the differences in the intensity of nuclear staining between low-grade versus malignant tumors were significant. These findings suggest that survivin is widely expressed in benign, borderline, and malignant serous tumors but that nuclear localization of survivin is more common in benign or borderline tumors than in malignant serous tumors of the ovary. The molecular mechanisms that determine the subcellular distribution of this protein may reflect the role of survivin in the regulation of apoptosis during the processes of malignant transformation.