Abstract Background. Diaphragm involvement by ovarian cancer is often considered to be a major obstacle to successful cytoreductive surgery. Lack of evidence of survival benefit, concerns over safety and lack of experience are common justifications for this belief. In this study, we sought to evaluate the therapeutic value of diaphragmatic surgery in advanced ovarian cancer. Methods. Relevant data from all consecutive patients with stage IIIC and IV epithelial ovarian cancer, primarily operated at Mayo Clinic from 1994 through 1998, were collected and analyzed. Statistical analyses were performed using χ 2 test, Cox regression model and Kaplan–Meier curves including log rank test. For comparison of trends in performing procedures, an additional 91 consecutive patients undergoing surgery from August 1, 2002 and August 31, 2004 were analyzed. Results. 244 eligible patients were identified. Mean age was 64 years (range: 24–87), and 5-year overall survival (OS) was 31.5%. For the entire cohort, residual disease (RD) was the only independent prognostic factor in multivariate analysis ( P < 0.0001) when considering other factors including demographic, intraoperative findings and procedures performed. For the subgroup of patients with tumor involving the diaphragm ( N = 181), patients who underwent diaphragm surgery (stripping of the diaphragmatic peritoneum, full or partial thickness diaphragm resection, excision of nodules or CUSA) had improved 5-year OS relative to those that did not (53% vs. 15%; P < 0.0001). Furthermore, in multivariate analysis of patients with diaphragm disease, both RD and performance of diaphragm surgery were independent predictors of outcome ( P < 0.001). Considering the subgroup of patients with RD < 1 cm, we noted a strong survival advantage for those patients who underwent diaphragm surgical procedures (5-year survival: 55% vs. 28%; P = 0.0005). Over time, we noted a statistically significant increase in the rate of diaphragm procedures for patients with diaphragm involvement from 1994–98 relative to 2002–3 (22.5% vs. 40%: P = 0.022). Conclusions. Surgical procedures to treat diaphragm disease increase the rate of complete and optimal debulking and correlate with improved survival even compared to patients optimally debulked without diaphragm surgery performed.