Dysregulation of the cell cycle is an important prerequisite for cancer development. p27 has an established role in cell cycle control and hence may be disrupted during carcinogenesis. The influence of p27 expression, including its subcellular location, on tumor behavior in ovarian cancer has been controversial. The purpose of this study was to evaluate the expression of p27 in a large population of patients with ovarian cancer and correlate this to clinicopathologic variables including overall survival. Using a tissue microarray of 339 primary ovarian cancers, the expression of p27 was assessed immunohistochemically. Coupled to a comprehensive database of clinicopathologic variables, its effect on these factors and survival was studied. Cytoplasmic p27 showed a progressively negative impact on overall survival (P=0.004). Tumors displaying nuclear p27 also had poorer prognosis (P=0.014). Factors shown to predict prognosis independently of each other were age, stage, and the absence of macroscopic disease after surgery. Cytoplasmic p27 expression, but not nuclear, was independently predictive of prognosis on multivariate analysis (P=0.042). Both subcellular locations of p27 expression were more frequently observed in serous compared with mucinous subtypes. Cytoplasmic p27 independently predicts poorer prognosis in ovarian carcinoma. These results seem counterintuitive, when considering the antiproliferative role of p27, but may reflect a more complex function of p27 within cell cycle regulation. These data support a novel role for p27 within the cytoplasm, possibly through effects on apoptosis, cellular motility, and drug resistance.