CD24 is a small heavily glycosylated glycosylphosphatidylinositol-linked cell surface protein, which is expressed in hematological malignancies as well as in a large variety of solid tumors. Very recently its expression in ovarian cancer has been found on RNA level by chip analysis. We evaluated CD24 protein expression by immunohistochemistry in 9 normal ovaries and 69 epithelial ovarian tumors (5 adenomas, 8 borderline tumors, and 56 carcinomas) with known follow-up data. Surface epithelium of normal ovaries as well as adenomas did not express CD24. In borderline tumors CD24 was expressed in membrane in 75% of cases, whereas cytoplasmic expression was detected in only one of nine cases. In invasive ovarian carcinomas, a membranous expression was detected in 84% and a cytoplasmic expression in 59% of cases. In univariate survival analysis of all invasive ovarian carcinomas, a highly significant association of increased cytoplasmic CD24 expression with shortened patient survival (mean 98 months versus 37 months, P = 0.0002, log rank test) was demonstrated. Other significant prognostic parameters were International Federation of Gynecology and Obstetrics (FIGO) stage, Silverberg grade, patient age, undifferentiated histological type, and metastatic disease. We did not detect a significant correlation of CD24 with these clinicopathological parameters. In multivariate analysis, only CD24 and FIGO stage were independent prognostic parameters. Our data suggest that the expression of CD24 as detected by immunohistochemistry is a new independent molecular marker for shortened survival time of patients with epithelial ovarian carcinomas.