Antenatal ultrasound at 36 weeks gestational age revealed a loculated fluid collection posterior to the urinary bladder in a female fetus. Follow up postnatal scans on day 2 and day 35 of life was performed. No collection was seen on day 2 whereas a small fluid collection in the vaginal canal was seen on day 35. No associated urogenital anomaly was detected. The distal vaginal canal was normal and the diagnosis of isolated hydrocolpos was made due to an imperforate hymen.