OBJECTIVE: Type I epithelial ovarian cancers (EOCs) are reported to be relatively chemoresistant. This study sought to compare pretreatment chemoresponse assays in Type I vs. Type II EOCs. STUDY DESIGN: 383 women with stage III-IV EOC enrolled in an observational study, with known chemoresponse assay results for 7 common therapeutic agents, were included. Type I EOCs were defined as grade 1 serous/endometrioid cancers and all clear cell/mucinous cancers. Type II EOCs were classified as grade 2-3 serous/endometrioid cancers and undifferentiated cancers. Chemotherapy assay responses were classified as sensitive (S), intermediately sensitive (I), or resistant (R). All patients were treated with platinum/taxane therapy following cytoreductive surgery. RESULTS: Thirty (7.8%) tumors were classified as Type I EOC, and 353 (92.2%) as Type II EOC. Type I patients were younger at the time of diagnosis (median age: 57 vs. 62 years, p=0.018) and had longer survival compared to Type II patients (mPFS: 25.8 vs. 16.4 months, HR=1.71, p=0.042). Eighty-six percent of Type I EOC specimens demonstrated a sensitive chemoresponse assay result to at least 1 agent; 35.7% were pan-S to all 7 agents. After adjusting for stage, debulking status, and type of EOC, multi-drug resistance was twice as likely in women with Type I EOC compared to Type II EOC (pan-R, 14.3% vs. 6.8% (p=0.268); pan-S, 35.7% vs. 51.2% (p=0.183)), but did not attain statistical significance. CONCLUSION(S): The majority of women with Type I EOC displayed assay sensitivity to at least one agent. Given the small sample size these findings need to be evaluated further.