OBJECTIVES:To determine the relationship of the time from surgery to intraperitoneal (IP) chemotherapy (TSIC) initiation with survival of patients with stage III epithelial ovarian cancer (EOC) patients using ancillary data from cooperative group clinical trials. METHODS:Data from 420 patients with stage III EOC treated with IP chemotherapy under GOG-0114 and 172 were reviewed. The Cox proportional hazards model was used to evaluate independent prognostic factors and estimate their covariate-adjusted effects on PFS and OS. RESULTS:The median TSIC was 62.5days (interquartile range 28-83). The median TSIC was longer for patients in GOG-0114 vs those in GOG-172 (83 vs 26days, p<0.001). TSIC was significantly associated (p=0.049) with PFS: each 10% increase in TSIC (days) decreases the risk of progression by 3%. TSIC was not significantly associated with OS in this model. In a linear regression model, gross residual disease was significantly associated with shorter TSIC (R2 -0.141, 95%CI -0.217, -0.064, p<0.001). When only data from GOG-172 were considered, no statistical significant association was found between TSIC and PFS or OS. CONCLUSIONS:In this ancillary data study, TSIC was not associated with improved OS in patients with stage III epithelial ovarian cancer. TSIC was significantly associated with PFS for the entire cohort, suggesting increase in PFS with longer TSIC. However, this was not found when only data from GOG 172 or GOG 114 were analyzed separately. Hence, the relationship between IP chemotherapy initiation and time from surgery needs to be studied further.