Background: Regarding the significance of neonate weight estimate and certain complications due to inaccuracy in estimation and controversy over use of sonography or clinical techniques, this study was carried out on clients referring to Booali hospital in Tehran during the years 2003-2004. Materials and Methods: The Study was a cross-sectional research performed on 300 qualified pregnant women (Over 38 weeks of pregnancy). Estimation of fetal weight through clinical method was done using fundal height and standard measurement, while estimation of fetal weight through sonography was carried out by the physician using head and abdominal circumference, femur length and the corresponding formula. The cases were then followed up and their weights at birth were measured precisely. Acceptable estimates for values were 10% ± real weight and 200 gr± real weight at birth for each method. The data were analyzed through and Fisher’s exact test. Results: The research was carried out on 300 qualified pregnant women in the age range of 26 ± 5.4 and pregnancy age of 39.3±1.1 weeks and body mass index (BMI) of 24 kg/m2. Real body weight of neonates at birth was 3229 gr ± 416.7 with 3.7% over 4000 gr, 2% under 2500 gr and the rest between 2500 gr to 4000 gr. In clinical method 74.6% and in sonography 89.3% of estimates were acceptable based on the scale of 10% ± real weight (P=0.0005). The above mentioned methods with the scale of 200 real weight were acceptable as 51.6% and 78.3% respectively (P=0.0005). Weight estimate by sonography in neonates under 4000 gr was preferable to clinical method while estimate by clinical method was more accurate in neonates over 4000 gr. (P=0.0005) Conclusion: Concerning the extent of accuracy, some adverse effects, cost and time consumed to estimated weight in sonography it would be advisable to use clinical method under normal cricumstances and sonography in some certain situations.