To date, there are no prognostic factors in ovarian cancer that adequately account for tumor biology and disease behavior. In recent years, some reports have described the prognostic significance of the amplification and overexpression of the oncogene c-erb B2 in various human cancers. Concerning ovarian cancer, this is still a matter of discussion. In the present study, tumor tissue of 275 patients treated for ovarian cancer at the Department of Obstetrics and Gynecology of the University of Gottingen between 1982 and 1992 was immunohistochemically analyzed for overexpression of c-erb B2− encoded transmembrane protein p185. In 19% (51 of 275 cases), p185 overexpression was detected. The percentage of p185-positive cases varied from 7 to 46% according to histological subtype. Correlation with tumor stage and the degree of histological differentiation was not observed. Patients with p185− positive tumors had a significantly worse prognosis (p = 0.001); median survival was 20 months compared with 33 months for p185-negative tumors. In the Cox proportional hazards regression, p185 overexpression was identified as an independent prognostically relevant factor. These results suggest that overexpression of oncogene c-erb B2 in ovarian cancer characterizes a group with unfavorable tumor biology and a significantly worse prognosis.