OBJECTIVE: Recurrence following primary platinum-based chemotherapy remains a challenge in the treatment of patients with advanced-stage epithelial ovarian cancer. This study examines whether a chemoresponse assay can identify patients who are platinum-resistant prior to treatment. STUDY DESIGN: Women (n = 276) with International Federation of Gynecology and Obstetrics stage III-IV ovarian, fallopian, and peritoneal cancer were enrolled in an observational study, and the responsiveness of their tumors was evaluated using a chemoresponse assay. All patients were treated with a platinum/taxane regimen following cytoreductive surgery. Assay responses to carboplatin or paclitaxel were classified as sensitive, intermediate sensitive (IS), or resistant. Association of assay response with progression-free survival (PFS) was analyzed using the Kaplan-Meier method and a Cox regression model. RESULTS: Patients whose tumors were resistant to carboplatin were at increased risk of disease progression compared to those with nonresistant (sensitive + IS) tumors (median PFS: 11.8 vs 16.6 months, respectively, P < .001), and the association was confirmed after adjusting for other clinical factors (hazard ratio, 1.71; 95% confidence interval, 1.12-2.62; P = .013). Association of assay response to paclitaxel with PFS trended in multivariate analysis (hazard ratio, 1.28; 95% confidence interval, 0.84-1.95; P = .245). For tumors resistant to carboplatin, 59% were sensitive or IS to at least 1 other commonly used agent, demonstrating the ability of the assay to inform treatment decisions beyond the standard platinum/taxane regimen. CONCLUSION: Assay resistance to carboplatin is strongly associated with shortened PFS among advanced-stage epithelial ovarian cancer patients treated with carboplatin + paclitaxel therapy, supporting use of this assay to identify patients likely to experience early recurrence on standard platinum-based therapy.