Objective: The aim of this study was to assess the importance of appendectomy during surgery for mucinous ovarian cancer. It can be difficult to distinguish between primary ovarian and primary appendiceal cancers clinically, histologically, and immunohistochemically. Removal of the appendix may facilitate differential diagnosis, improve staging, and possibly increase 5-year survival but may also be associated with increased postsurgical morbidity. In the largest population published to date, we analyze and discuss these matters. Methods: Prospectively gathered data on 269 patients with confirmed mucinous ovarian adenocarcinoma from a national database were analyzed. The impact of appendectomy and metastases to the appendix on 5-year and overall survival was analyzed. Results: Appendectomy was performed in 172 cases (64%), and in 10 cases (4%), pathologic evaluation of the removed appendix revealed metastases from ovarian cancer. Three of the cases were macroscopically normal, and metastases were discovered only during microscopic evaluation. Patients with metastatic disease to the appendix had significantly worse 5-year survival (22%) compared with patients without metastases (73%) (χ² = 31.998, P < 0.0001). Equally, 5-year survival was significantly higher in patients who had been adequately staged with hysterectomy, omentectomy, bilateral salpingo-oophorectomy, and appendectomy (74% vs 52%, χ² = 7.322, P = 0.007). In multivariate analysis, increase in revised 2013 International Federation of Gynecology and Obstetrics classification stage (IA reference) was significantly associated with worsened prognosis (hazard ratio, 1.13; P < 0.0001). Equally, each stepwise increase in performance status score was related to a poorer prognosis with hazard ratio of 1.63 (P < 0.0001). Metastases to the appendix and staging did not remain significant factors of survival in multivariate analysis. Conclusions: Univariate analysis suggests that metastatic disease to the appendix and failure to perform complete staging including appendectomy are related to a worsened prognosis. A normal-looking appendix does not exclude metastatic disease, and because appendectomy is easily performed and does not increase morbidity, it should be performed during surgery for suspected mucinous ovarian cancer.