OBJECTIVE To evaluate the changes of pain symptoms induced by buserelin acetate, a gonadotropin-releasing hormone agonist, in a group of patients with endometriosis. METHODS Thirty-five infertile patients with one or more of the following symptoms (dysmenorrhea, pelvic pain, deep dyspareunia, and endometriosis stage I or II) were allocated randomly to treatment with buserelin acetate 1,200 micrograms/d IN for 6 months (n = 19) or expectant management (n = 16). Pain symptoms were recorded by the women themselves using a questionnaire that included two scales for pain evaluation: one analogue and one multidimensional. The treated and untreated patients were followed for a minimum of 18 and 12 months from the time of randomization, respectively. RESULTS Buserelin acetate markedly reduced dysmenorrhea, pelvic pain, and dyspareunia during the treatment and also for the 12 subsequent months. During follow-up of the expectant management group, dysmenorrhea resolved in 19% (3/16) of the cases, and pelvic pain did not recur after diagnostic laparoscopy in one of the three women affected nor did deep dyspareunia in two of the five who reported the symptom before laparoscopy. CONCLUSIONS Buserelin acetate induced a significant improvement of pain symptoms that persisted in approximately half of the patients even after withdrawal of the drug. However, symptoms associated with endometriosis showed a spontaneous remission in approximately one fifth of the untreated patients.