A 24-year-old primigravid women with no remarkable history and antenatal follow-up was referred to our clinic with the diagnosis of fetal megacystis. Ultrasound examination revealed an oval shaped hypoechoic cystic mass measuring 80×55×50 mm occupying the fetal pelvis in a female fetus. The fluid inside the cyst was heterogeneous giving a two level appearance. A normal looking urinary bladder was visualised separately which was located in normal position. Further sonographic evaluation revealed postaxial polydactyly in both hands. The fetal echocardiography and amniotic fluid index was normal. An obstetrical MRI was done for the suspicion of a hydrometrocolpos and confirmed the diagnosis. The infant was delivered by vaginal route at term. Physical examination of neonate confirmed postaxial polydactyly in hands. After birth a cystoscopy performed by the paediatric surgeons revealed a urogenital sinus and vaginal atresia. A catheter was placed in the uterine cavity to drain it. Nine months later the baby went on a 'vaginal pull through' operation to reconstruct the vagina and the urethra. The baby is now 3 years old and doing well.