Cumulative embryo score (CES) is one of the many embryo scoring methods which have been developed to help clinicians to transfer high quality embryos and predict pregnancy rate in assisted reproductive techniques (ART) cycles. Regarding the existing difference in CES calculation this study was done to compare two methods in order to determine the more practical and preferable one. In a retrospective, cross sectional descriptive analytical study, a total of 508 ART cycles in infertile patients treated from November 2002 until March 2004, were evaluated using two methods of CES calculation in embryonic scoring to predict ART outcome. According to one method, CES was obtained by adding the individual scores of all transferred embryos. Whereas in the other reference method, CES was calculated by the sum of each embryo score multiplied by its number of blastomeres on the day of transfer. The mean score of transferred embryos (MSTE) was referred to CES divided by the total number of embryos transferred in either method. A total of 109 clinical pregnancies (pregnancy rate 21.5%) including 96 singletons, 10 twins and triplets occurred in the 508 ART cycles. The pregnancy rate was strongly correlated to CES & MSTE. According to one method, CES was 12.6±6.4 in pregnant versus 9.2±5.8 in non-pregnant group (P