prediction and importance of severe postoperative complications after ovarian cancer surgery is a strong issue in patient selection and evaluation. Pre- and early peroperative predictors of severe 30-days postoperative complications (Clavien-Dindo class ≥3) after surgery for primary ovarian cancer are not fully established, neither their impact on patients’ survival. A prospective observational study included 256 patients with primary ovarian cancer FIGO stages IIB-IV, operated during 2009–2018 in a primary or interval debulking surgery setting. Patient variables were analysed in relation to severe postoperative complications (Clavien-Dindo class ≥3) and overall survival. High-grade postoperative complications occurred in 24.2% patients. Class 3a complications were observed in 12.5% cases. High-grade complications class ≥3 were observed in 31.6% after primary debulking surgery compared to 12.2% after interval debulking surgery (p = 0.0004). Peritoneal cancer index ≥21 and preoperative albumin concentration ≤33 g/L were independent predictors of high-grade complications. Peritoneal cancer index correlated with the surgical complexity score and completeness of cytoreduction. Increased peritoneal cancer index was a negative predictor of overall survival, but high-grade complications did not influence survival negatively. Peritoneal cancer index ≥21 was an independent predictor of high-grade complications after ovarian cancer surgery. Increased peritoneal cancer index also impacted overall survival negatively, but high-grade complications did not influence overall survival. •Peritoneal cancer index predicted high-grade postoperative complications.•High-grade postoperative complications did not impact overall survival negatively.•Peritoneal cancer index and surgical complexity score correlated positively.•High peritoneal cancer index correlated with incomplete cytoreduction.