INTRODUCTION. Epithelial ovarian cancer (OC) is the most fatal gynaecological cancer. The use of extensive surgical procedures implies the potential severity of post-operative complications. In Denmark, registration of complications has changed from manual database registration to data transfer from medical records to the Danish National Patient Registry (NPR). This study examines whether a new complication algorithm based on NPR data may be used to identify 30-day post-operative complications among patients with advanced stage IIIC–IV OC. METHODS. Complications were graded according to Clavien-Dindo (CD). The algorithm was validated in a cohort undergoing surgery at the OUH, between 1 January 2007 and 31 December 2012. The CD grades were sub-grouped into mild (CD 0-2) and severe (CD 3-5) complications for sub-analyses. RESULTS. A total of 330 patients were included. The overall sensitivity (SN) and specificity (SP) of the algorithm (CD 0-5) were 56.4% (95% confidence interval (CI): 48.0-65.0%) and 92.4% (95% CI: 86.5-93.0%), respectively, with an overall kappa coefficient (κ) of 0.43. For severe complications (CD 3-5), the algorithm had an SN of 74.2% (95% CI: 67.4-83.6%) and an SP of 97.4% (95% CI: 95.5-99.4%), with a κ of 0.65. CONCLUSIONS. The algorithm had a moderate SN and a high SP with substantial agreement regarding severe complications. A standardised registration of complications in the NPR will likely improve the algorithm's performance. FUNDING. The Danish Clinical Quality Program DKK 200,000. TRIAL REGISTRATION. Not relevant.