Imperforate hymen is a congenital anomaly in which the hymenal membrane has no opening with subsequent vaginal outlet obstruction. After maternal hormone stimulation there is an increased cervical mucous glands secretion, which gradually accumulates and expands forming a pelvic mass. Neonatal hydrometrocolpos is a dilatation of the vagina and uterus because of accumulation of secretions. A 39 + 4 weeks neonate was born by spontaneous vaginal delivery with normal antenatal scans. On day 2, she presented with irritability, poor feeding, abdominal tenderness and distention. Clinical examination revealed imperforate hymen with bulging of vaginal introitus. Subsequent abdominal ultrasound showed dilated vagina and uterus without urinary tract obstruction. The imperforate hymen was managed surgically with hymenal incision. Imperforate hymen is a rare but fearsome congenital disorder. Routine neonatal examination should include a careful inspection of the genitalia.