Fetal weight assessment is one of the basic principals of appropriate antenatal and intrapartal care. Ultrasound assessment is the most accurate and most often used method, but it is still unclear which of the many formulas used for the assessment is most accurate and most reliable. The aim of this study was to determine whether there is a difference between actual birth weight assessed after delivery and estimated fetal weight assessed using the ultrasound and two different formulas; Hadlock II and Campbell Wilkin formula. Furthermore, the purpose of this study was to recognize the protective and risk factors that influence the accuracy of fetal weight ultrasound assessment. This prospective study was done between December 10th 2013 and March 10th 2014 at KB «Sveti duh» in Zagreb. The study included 342 pregnant women who gave birth at the delivery ward and who had a fetal weight ultrasound assessment done within three days prior to delivery and documented in their medical history. The difference between actual and estimated birth weight was tested using the Wilcoxon Matched Pairs Test. The study found that there is no significant difference between acutal birth weight and estimated birth weight assessed using the Hadlock II formula, while a significant difference exists when the Campbell Wilkin formula is used. Also, the accuracy of fetal weight assessment is less accurate when used for extreme values of fetal weight, while body mass index, weight of the pregnant woman and gestational age do not influence the accuracy of fetal weight assessment. In conclusion, fetal weight ultrasound assessment using Hadlock II formula is an accurate and reliable method of assessment and should be used routinely in every day clincial practice. The Campbell Wilkin formula should be used with caution and exclusively when it is not possible to use the Hadlock II formula. Additionally, it is important to be more attentive when fetal weight is outside normal range because the assessment is less accurate in those cases and has limited value.