To compare the accuracy of three-dimensional (3-D) versus two-dimensional (2-D) ultrasonography (U/S) in the measurement of follicular volume and identification of cumulus oophorus complex, thirty women were selected. Women who undergoing ovarian stimulation for in-vitro fertilization and embryo transfer (IVF-ET) using the long protocol of GnRH agonist were scanned by 2-D and 3-D ultrasonography before follicular aspiration. The volume of aspirated follicular fluid was compared with corresponding volume measured by 3-D and 2-D ultrasonography. It was found that, the high accuracy of 3-D U/S measurement of follicular volume is demonstrated clearly by limits of agreement which were within 1 ml of the true volume. While, the 2-D U/S produced limits of agreement those were up to 3.5 ml above or 2.5 ml below the true volume. Also, 3-D U/S could identify cumulus oophorus complex in 86% of cases. From this study, it was concluded that 3-D U/S system is more accurate than 2-D U/S in the measurement of the true follicular volume. Also, 3-D U/S is superior to 2-D U/S for identification of cumulus oophorus complex.