Objective: To investigate the prevalence of empty follicle syndrome (EFS), a condition in which no oocytes were retrieved after ovarian stimulation, categorized into genuine EFS (g-EFS) and false EFS (f-EFS), at the King Chulalongkorn Memorial Hospital (KCMH), Thailand. Materials and Methods: A retrospective study was conducted at the infertility clinic of the KCMH. Medical records of the assisted reproductive technology (ART) patients between January 2001 and October 2019 (5,523 patients) were reviewed. Exclusion criteria were the cases where ovulation occurred before oocyte retrieval or the cases with less than four follicles larger than 14 mm diameter on the day of triggering ovulation to minimize the absence of oocyte from the poor response. The patients with EFS, g-EFS, which are EFS with detectable urinary human chorionic gonadotropin (hCG), and f-EFS, which are EFS with undetectable urinary hCG, were identified. Prevalence of EFS was calculated. Results: There were three cases with EFS in the present study, which g-EFS was identified in one case and f-EFS in two cases. The prevalence of EFS was 0.054%, which g-EFS was 0.018% and f-EFS was 0.036%. Conclusion: EFS is a rare condition, particularly the g-EFS. Although EFS is rare, it causes tremendous stress and anxiety to both patients and physicians. Further study in the etiopathogenesis of EFS is required. Keywords: Empty follicle syndrome; Infertility; In vitro fertilization