Ovarian cancer spreads early in the disease into the abdomen. An en bloc resection of the tumor, according to surgical principle, is not possible in patients with high-stage ovarian cancer. At surgery, large pelvic tumor lesions are found together with multiple tumor lesions involving the omentum, bowel, and mesentery together with a diffuse peritoneal carcinomatosis and diaphragmatic involvement. A multimodality approach with cytoreductive surgery and taxol platinum-based chemotherapy is therefore the mainstay of treatment of advanced ovarian cancer. The size of residual disease after surgery is one of the most important prognostic factors for survival. Patients with an optimal tumor cytoreduction (residual lesions smaller than 1 cm) have a significant longer survival (almost two times the median survival) than patients with larger residual lesions. This holds true even for patients with International Federation of Gynecology and Obstetrics (FIGO) stage IV disease. Patients in whom all macroscopic tumor is resected do have the longest survival. The 2-year survival of patients with a radical resection of all macroscopic tumors is 80%, in contrast to less than 22% for the patients with lesions larger than 2 cm. An optimal primary cytoreductive surgery can generally be performed in 30% to 50% of patients. Only in more experienced gynecologic oncology centers is the percentage as high as 85%, but sometimes at the cost of an increased morbidity and even mortality. The worse prognosis of the patients with a suboptimal primary cytoreductive surgery can be improved by an interval cytoreductive surgery after platinum-containing induction chemotherapy. The median survival and progression-free survivals are significantly lengthened by cytoreductive surgery. After more than 5-years follow-up there is still a significant survival benefit: the 5-year survival of the surgery patients was 24% versus 13% for the no-surgery patients (P = 0.0032). All patients, including those with unfavorable prognostic factors (stage IV disease, peritonitis carcinomatosis, or ascites at primary surgery), and even patients with stable disease after induction chemotherapy, seem to benefit from interval cytoreductive surgery. The increase in progression-free survival and overall survival does outweigh the morbidity associated with interval debulking surgery, which is not different from those associated with primary surgery.