OBJECTIVE To assess the clinical course of obstructive Müllerian anomalies found in girls after menarche. METHODS A retrospective case series of adolescents who, between 2009 and 2016, were treated for vaginal or uterine obstructive malformations diagnosed after menarche. METHODS Division of Gynecology, Poznań University of Medical Sciences, Poznań, Poland. METHODS Twenty-two patients who, at the age range between 11.4 and 18.2 (median, 13.1) years, between 2 and 74 (median 7.5) months after menarche, underwent surgical repair of obstructive genital anomaly. METHODS Müllerian defect type, presentation, radiologic findings, pre- and postoperative course. RESULTS Eighteen patients (18 of 22; 81.8%) were diagnosed with obstructed hemivagina ipsilateral renal anomaly syndrome. One patient (1 of 22; 4.5%) was diagnosed with uterus didelphys and unilateral cervical atresia. Three patients (3 of 22; 13.6%) had unicornuate uterus with a cavitated, noncommunicating rudimentary horn. The right side was affected in 13 patients (13 of 22; 59.1%), and the left side in 9 patients (9 of 22; 40.9%; P > .05). All but 1 patient had renal agenesis on the side of obstruction. Before repair of the obstructive genital anomaly, 4 patients underwent unnecessary surgeries for misdiagnosed ovarian cysts. Serious complications (pelvic inflammatory disease, vesicovaginal fistula) occurred in 2 patients with microperforated pyocolpos. Pelvic endometriosis was found in 4 of our patients. CONCLUSIONS Our case series suggests that obstructed hemivagina ipsilateral renal anomaly syndrome is the most common obstructive Müllerian anomaly diagnosed in adolescents after menarche. The differential diagnosis for unilateral kidney agenesis accompanied by dysmenorrhea in adolescent girls should include obstructive genital tract anomaly. Accurate diagnosis of an obstructive genital anomaly early after menarche might help prevent unnecessary surgeries and infection-related complications. Meanwhile, prompt surgical correction of an obstructive genital tract anomaly results in relief of symptoms and might reduce the risk of endometriosis.