Objective: The value of surgical staging of apparent early stage epithelial ovarian carcinoma (EOC) is unclear. The aim of this study was to evaluate the importance of surgical staging on the stage of disease and treatment plan. Material and methods: All patients with apparent stage I EOC undergoing staging from 01/01/2005 to 30/06/2017 in all Danish hospitals and in the Radboud University Hospital Nijmegen, the Netherlands, were evaluated to identify the pathological findings responsible for upstaging and changes in treatment plans. Results: We included 1234 patients with apparent stage I EOC. The staging steps often missed were the biopsy from the right diaphragmatic surface (missed in 96.9% of all patients) and lymph node (LN) sampling or lymphadenectomy (missed in 65.5% of all patients). Upstaging occurred in 393 patients (31.8%) due to microscopic spread to both ovaries (0.8%); ovarian surface (5.8%); positive cytology (10.0%); fallopian tubes (3.1%), ovary (1.5%) and/or uterus serosa (1.2%); pelvic peritoneum (4.3%); LNs (4.7%); omentum (3.7%); abdominal peritoneum (0.6%) and right diaphragmatic surface (2.6%). Of the 393 upstaged patients, 138 (35.1%) had an altered treatment plan due to metastases found by surgical staging. Conclusion: Staging was incomplete in most patients, mainly because a biopsy of the diaphragm was omitted. However, surgical staging led to adjuvant treatment in 35.1% of the upstaged patients. Peritoneal biopsies (para-colic gutters and right diaphragm) were of little value, since few patients had an adjustment of treatment plan due to these biopsies. Omitting these biopsies, in the absence of peritoneal abnormalities, is justifiable.