Expression of mdm-2 mRNA was measured in 90 ovarian-cancer tissue specimens using the S1 nuclease assay, to investigate a possible association between MDM2 expression and prognosis. mdm-2 mRNA expression was an independent prognostic factor for patients with primary ovarian cancer, FIGO (International Federation of Gynecology and Obstetrics) stages III and IV (n = 57), who all received chemotherapy with carboplatin or cisplatin and cyclophosphamide. Median survival time for patients (FIGO stages III and IV) with no detectable expression of mdm-2 mRNA (n = 14) was 171 days, as compared with 839 days for patients (n = 43) with detectable mdm-2 mRNA (p = 0.0194; log-rank test). However, no association between mdm-2 mRNA expression and survival was observed for patients with FIGO stages I and II who did not receive chemotherapy. mdm-2 expression was not associated with FIGO stage, residual disease, histologic grade and type. Our results suggest that mdm-2, which is known to disrupt p53 function, sensitizes ovarian-cancer cells to cisplatin/cyclophosphamide, possibly by inhibition of p53-mediated G1 cell-cycle arrest and p53-stimulated nucleotide-excision repair.