Ultrasound examination of the fetal perineal area was done in third trimester ofpregnancy to determine the fetal sex. We carried out ultrasound on 621 consecutiveobstetrics patients who attended these centers for obstetric causes referred by theirphysicians. Of them 612 had singleton pregnancy and 9 had twin pregnancy. Weattempted to determine the sex of all fetuses (n=630) based on demonstration of maleand female genitalia. In 585 pregnancies, fetal genitalia were well visualized – theaccuracy rate was thus 92.9%, while the rest 7.1% (n=45) could not be determinedwhich was limited by fetal presentation, position, volume of amniotic fluid and colonicgas. Among the correctly determined cases 384 (65.6%) were male and the rest 201(34.4%) were female. About 91% of the mother desired a male child in contrast toonly 3.1% of the mother who desired a female child prior to ultrasound examination.Interesting enough mothers welcoming female child were all multigravida with previousmale child/children. It needs to mention here that no primae mother welcomed femalechild. Some other aspects of prenatal sex determination have also been discussed inthisarticle.Key Words: Ultrasound, Fetal sex, Bangladesh