OBJECTIVE: To evaluate the association between the endometriosis phenotype and the age at menarche. DESIGN: An observational, cross-sectional study using prospectively collected data (Canadian Task Force classification II-2). SETTING: Single university tertiary referral center. PATIENTS: To be eligible, women had to have undergone their 1st complete surgical exeresis of endometriotic lesions. For each patient, a standardized questionnaire was completed the month before the surgery. Endometriotic lesions were classified into 3 phenotypes: superficial peritoneal endometriosis (SUP), endometrioma (OMA), or deep infiltrating endometriosis (DIE). Patients were divided into 3 groups: early menarche (< 12 years), typical menarche (≥ 12 and ≤ 13 years) and late menarche (> 13 years). The groups were compared in terms of general characteristics, medical history, disease phenotype, and disease severity. INTERVENTIONS: Surgical management for a benign gynecologic condition. MAIN OUTCOME MEASURE(S): Correlation between the endometriosis phenotype and the age at menarche. MEASUREMENTS AND MAIN RESULTS: From January 2004 to December 2016, 789 women with histologically confirmed endometriosis were enrolled in the study. The mean age at menarche was 12.9 ± 1.6 years of age, (range 9 to 18). The mean age at menarche and the mean time interval between menarche and the 1st surgery for endometriosis were not significantly different between the three phenotypes (SUP, OMA, DIE). When women with early menarche, typical menarche, or late menarche were compared, no differences were observed in terms of the endometriosis phenotype and the anatomical distribution of the endometriotic lesions. CONCLUSION: For women operated for the first time for endometriosis, age at menarche is not associated with the disease phenotype.