Objective: To determine the duration of time to the recurrence of pain attributable to endometriosis after the discontinuation of treatment with danazol or a GnRH agonist (GnRH-a) in patients who have had a satisfactory response to the treatment. Design: Retrospective study. Setting: Nine academic medical centers in three countries. Patient(s): Three hundred twenty-seven women with diagnosed and staged endometriosis who were treated with at least 6 months of danazol or a GnRH-a and who experienced significant pain relief with therapy. Intervention(s): None. Main Outcome Measure(s): Duration of pain relief after completion of treatment as determined by a patient-initiated report of pain recurrence or increase in pain severity requiring intervention. Result(s): The median time to the recurrence of pain was 6.1 months for patients treated with danazol and 5.2 months for patients treated with a GnRH-a. Conclusion(s): Although there was a lack of uniformity in treatment effects across sites, the analyses have taken into account major covariant effects. The time to the recurrence of endometriosis-associated pain after danazol treatment was slightly longer than that after GnRH-a treatment.