This study aims to investigate the relationship between comprehension, based on the problem triggers as an indicator, and accuracy, based on the criterion of omission during English-Arabic simultaneous interpreting. In these cases, the less comprehension, the more omissions in the interpretation, the lower the accuracy. The performances of 5 MA students at the Department of Translation, College of Arts, University of Mosul, are transcribed and analyzed using the hybrid model of Larson’s (1984) “Translation Quality Assessment” and Gile’s (2009) “Effort” Models. Having analyzed the accuracy of the interpretations, a significant number of omissions were noticed due to inappropriate allocation of the processing capacity for comprehension. The study concludes that comprehension is the essential processing capacity effort and a vital determinant of the accuracy of the interpretation. The different levels of exercising the comprehension processing capacity measured by the SL problem triggers lead to different accuracy levels starting with high accuracy and ending with inaccuracy.