- OBJECTIVE: To determine which descriptors of cytoreductive surgical extent in advanced ovarian cancer(AOC) best predict post-operative morbidity. DESIGN: Retrospective notes review. SETTING: A gynaecological cancer centre in the United Kingdom. POPULATION: 608 women operated on for AOC in 114 months at a tertiary cancer centre between 16/8/07-16/2/17. METHODS: Outcome data were analysed by six approaches to classify extent of surgery. Standard/ultra-radical surgery; standard/radical/supra-radical surgery; presence/absence of gastrointestinal resections; low/intermediate/high surgical complexity score(SCS); presence of bowel anastomoses and/or diaphragmatic surgery; and presence/absence of multiple bowel resections. MAIN OUTCOME MEASURES: Major (grade 3-5) post-operative morbidity and mortality. RESULTS: 43(7.1%) patients experienced major complications. Grade 5 complications occurred in 6 patients(1.0%). Patients who underwent multiple bowel resections had a relative risk(RR) of 7.73(95%CI 3.92-15.26), high SCS RR of 6.12(95%CI 3.25-11.52); diaphragmatic surgery and gastrointestinal anastomosis RR 5.57(95%CI 2.65 - 11.72); "any gastrointestinal resection" RR 4.69(95%CI 2.66-8.24); ultra-radical surgery RR 4.65(95%CI 2.26-8.79); supra-radical surgery RR 4.20(95%CI 2.35-7.51) of grade 3-5 morbidity as compared to those undergoing standard surgery as defined by NICE. No significant difference was seen in the rate of major morbidity between standard (6/59,10.2%) and ultra-radical (9/81,11.1%) surgery within the cohort who had intermediate complex surgery (p>0.05). CONCLUSIONS: Numbers of procedures performed significantly correlates with major morbidity. The number of procedures performed better predicted major post-operative morbidity than the performance of certain "high risk" procedures. We recommend the SCS to define a higher-risk operation. NICE should re-evaluate the use of the term "ultra-radical" surgery.