Introduction: An imperforate hymen is a rare congenital condition that typically presents at puberty with cyclical abdominal pain and primary amenorrhea, and occasionally acute urinary retention due to hematocolpos. We report a young girl who presented to a Paediatric unit with acute urinary retention without preceding cyclical pain, highlighting the importance of careful examination. Case presentation: A 12-year-old previously healthy girl presented with acute urinary retention for 24 hours, preceded by two days of dribbling and difficulty initiating micturition. She complained of lower abdominal pain with visible distension. She had not yet attained menarche and denied any history of cyclical abdominal pain. There were no neurological symptoms, and systemic examination was unremarkable. Local examination revealed a tense, bluish, 3×3 cm bulge inferior to the urethral meatus, with the vaginal opening not visible. An urgent abdominal ultrasound demonstrated an 8×9 cm homogeneous cystic lesion located posterior to the bladder, communicating with the cervix, suggestive of hematocolpos. Following urethral catheterization, 750 mL of urine was drained, relieving the acute retention. Based on clinical and ultrasonographic findings, a diagnosis of imperforate hymen with hematocolpos was made. An urgent Gynecology referral was done and surgical interventionwas performed under general Anesthesia. A cruciate incision was made over the bulging hymen, evacuating approximately 400mL of retained blood-stained fluid. The patient recovered uneventfully . Conclusion: Hematocolpos should be considered in adolescent girls with acute urinary retention. Although Magnetic Resonance Imaging is ideal, timely clinical assessment and ultrasonography enabled successful diagnosis and management in a low-resource hospital setting.