['Cyclooxygenase-2 (COX-2) expression is associated with aggressive clinicopathological parameters and unfavourable prognosis in several human malignancies. The aim of this study was to investigate the expression of COX-2 and its association with clinicopathological parameters, response to treatment, and clinical outcome in ovarian cancer patients.', 'COX-2 expression was analysed by immunohistochemistry in 87 primary ovarian carcinomas from patients with measurable disease after primary laparotomy.', 'COX-2 immunoreaction was observed in 39 (44.8%) cases, and did not differ in distribution according to age, FIGO stage, debulking at time of surgery, presence of ascites, histotype or tumour grade. Both in patients cytoreduced at first surgery and in those undergoing only explorative laparotomy, the percentage of COX-2 positivity was significantly higher in non-responding than in patients responding to treatment (P = 0.043 and P = 0.0018, respectively). In multivariate analysis, only COX-2 positivity and older age retained an independent role in predicting a poor chance of response to treatment. There was no significant difference of clinical outcome according to COX-2 status in patients undergoing primary debulking while, in the subgroup of patients who underwent explorative laparotomy, COX-2-positive cases showed a shorter time to progression (P = 0.025) and overall survival (P = 0.025).'] Is increased cyclooxygenase-2 ( COX-2 ) expression associated with chemotherapy resistance and outcome in ovarian cancer patients?