Much has been written concerning the potential group differences in responding to multiple-choice achievement test items. This discussion has included references to possible disparities in tendency to omit such test items. When test scores are used for high-stakes decision making, even small differences in scores and rankings that arise from male and female students' different tendencies to omit may have serious consequences and are important to examine. The data for this study were obtained from an Iowa Testing Programs database that contains the responses of students who took the Iowa Tests of Basic Skills (ITBS) or the Iowa Tests of Educational Development (ITED) in the state of Iowa. Approximately 430,000 Iowa students in the 3rd, 7th, and 11th grades who took the ITBS or ITED during 1980-1981, 1985-1986, 1990-1991, 1995-1996, or 2000-2001 were included in the study. Unlike other studies of omitting tendency, this study demonstrated that differential tendencies to omit between the sexes have not had an important impact on mean score differences in achievement between the sexes in the past 20 years.