BACKGROUND Patients with endometriosis (EMs) are routinely advised to take GnRH-a for 3-6 months to improve the internal reproductive environment, but this may not be necessary. MATERIAL AND METHODS This retrospective study examined the effects of in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) with shortened (n=311) or conventional (n=213) long-term pituitary downregulation in EMs patients between January 2013 and July 2017. RESULTS The 2 groups showed no significant differences in gonadotropin (Gn) dose, number of oocytes retrieved, or miscarriage rate. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) levels on the initiation day and the LH level on human chorionic gonadotropin (hCG) day (1.22±1.39 vs. 0.74±0.55 P=0.0026) were higher in the study group than in the control group. The cumulative live birth rates in the second cycle were 69.13% in the study group (95% confidence interval (CI), 64-74.27%) vs. 68.54% in the control group (95% CI, 62.31-74.78%, P=0.88, respectively). CONCLUSIONS This study showed that the shortened regimen and the ultralong regimen did not produce different pregnancy outcomes after ART, and the single-application, long-term GnRH-a protocol may serve as a cost-effective and safe treatment protocol for EMs patients.