To determine the impact of chemotherapy dose reductions and dose delays on progression-free survival (PFS) in women with ovarian cancer receiving first line chemotherapy in a real world prospective cohort study. Patients with newly diagnosed epithelial ovarian (or peritoneal, fallopian tube) cancer enrolled in a national Australian prospective study, OPAL, who commenced three-weekly carboplatin (AUC 5 or 6) and paclitaxel 175 mg/m2 (CP) or carboplatin (AUC 5 or 6) and dose-dense weekly paclitaxel 80 mg/m2 (DD-CP) were eligible. Primary endpoint was PFS. 634 evaluable patients, 309 commenced CP and 325 DD-CP. Patient's age was similar in the two groups (median 62 years, range 21–79). All planned chemotherapy doses were completed by 66% vs 40% (p < 0.001) in the CP and DD-CP groups respectively. There was at least one treatment delay in 28% vs 58% (p < 0.001) in the CP and DD-CP groups, respectively, and 29% vs 49% (p < 0.001), respectively, required at least a 15% dose reduction for either carboplatin or paclitaxel. Median PFS was 29.2 22.9, 43.8 and 21.5 19.4, 23.1 months in the CP and DD-CP groups respectively. Adjusting for age, histology and FIGO stage PFS did not differ between treatment groups. Median PFS was similar in patients irrespective of dose reduction or dose delay. Patients receiving DD-CP required more dose reductions and delays due to haematological toxicities and lower completion rates than CP without significant difference in median PFS between CP and DD-CP. Median PFS was similar in patients irrespective of dose reduction or dose delay. •Dose modifications are common for haematological and neurological toxicity with Carboplatin and Paclitaxel.•Progression free survival was not impacted irrespective of dose reduction or dose delay.•More haematological toxicities experienced with dose dense chemotherapy.•High rates of chemotherapy completion with three-weekly Carboplatin and Paclitaxel