Background:Incomplete surgical staging is a negative prognostic factor for patients with borderline ovarian tumours (BOT). However, little is known about the prognostic impact of each individual staging procedure.Methods:Clinical parameters of 950 patients with BOT (confirmed by central reference pathology) treated between 1998 and 2008 at 24 German AGO centres were analysed. In 559 patients with serous BOT and adequate ovarian surgery, further recommended staging procedures (omentectomy, peritoneal biopsies, cytology) were evaluated applying Cox regression models with respect to progression-free survival (PFS).Results:For patients with one missing staging procedure, the hazard ratio (HR) for recurrence was 1.25 (95%-CI 0.66-2.39; P=0.497). This risk increased with each additional procedure skipped reaching statistical significance in case of two (HR 1.95; 95%-CI 1.06-3.58; P=0.031) and three missing steps (HR 2.37; 95%-CI 1.22-4.64; P=0.011). The most crucial procedure was omentectomy which retained a statistically significant impact on PFS in multiple analysis (HR 1.91; 95%-CI 1.15-3.19; P=0.013) adjusting for previously established prognostic factors as FIGO stage, tumour residuals, and fertility preservation.Conclusion:Individual surgical staging procedures contribute to the prognosis for patients with serous BOT. In this analysis, recurrence risk increased with each skipped surgical step. This should be considered when re-staging procedures following incomplete primary surgery are discussed.