Endometriosis is a major cause of disability in women, and 40% to 50% of patients experience disease recurrence by 5 years after surgery. This multicenter retrospective cohort study (N = 588) determined the rate and risk factors for recurrent endometrioma after primary surgery and examined the role of postoperative hormone therapy. When recurrence was defined by sonographic identification of the endometrioma (>/=20 mm in size), 61 (10.4%) patients experienced disease recurrence. The cumulative recurrence rates at 1, 2, 3, and 5 years after surgery were 2.2%, 4.9%, 6.9%, and 9.8%, respectively. To determine the risk factors for recurrence, the clinical factors of patients with and without recurrence were compared. There was a significantly increased risk of recurrence with posterior cul-de-sac (PCDS) obliteration (P = .031) and higher serum cancer antigen 125 (CA125) level (P = .005). A longer postoperative hormonal therapy duration (P < .01), absence of PCDS obliteration (P = .036), and lower serum CA125 level (P = .014) were associated with longer recurrence-free interval on multivariate analysis using the Cox regression model. Postoperative hormone therapy prolonged the interval from the time of surgery to the first recurrence. However, it did not prolong the interval from the end of treatment to the first recurrence. Our results indicate that although long-term postoperative hormone therapy might maintain minimal disease status, it does not control residual disease. Therefore, persistent hormone suppression should be used to prevent disease recurrence.