To determine optimal sonographic fetal weight estimation formula for male and female infants, a prospective study has been performed. Uncomplicated pregnancies and 465 newborns were evaluated. Measurements included birth weight, length and head circumference in addition to fetal head circumference, femur length, abdominal circumference and biparietal diameter. Actual weights were compared with estimated weights calculated by ten different formula. Estimated fetal weight obtained from all formula, except those of Merz, Warsof and Ferrero, tended to be lower than the measured birth weight. The smallest mean differences were obtained with Hadlock 1, Hadlock 2, Hadlock 4 and Shepard formula (19 g-85 g), whereas Merz and Woo produced largest mean differences (110 g-364 g). Intraclass correlation coefficients (ICCs) generated with Hadlock 1 and Hadlock 2 formula were identical (0.90). ICCs obtained with Hadlock 3 and Hadlock 4, Shepard, Merz, Warsof and Campbell formula varied between 0.84 and 0.88. Hadlock 1 and 2 formula gave the closest approximation of birth weight in Turkish population. (c) 2005 World Federation for Ultrasound in Medicine & Biology.