Although student attrition and retention are researched all over the world, there is no final formula available to ensure academic success for selected students. The purpose is to share research undertaken at the Tshwane University of Technology (TUT) in order to investigate the role of mathematics in student achievement and retention in National Diploma engineering programmes. This study contributes to the identification of key aspects that exercise an influence on success at a University of Technology (UoT) in a country where students have diverse schooling experiences. An ex post facto study was carried out on a sample drawn from the first-time-entering National Diploma cohorts of 2009 and 2010 to determine a possible correlation between their National Senior Certificate (Grade 12) mathematics performance and their first semester mathematics performance, or with their first semester mathematics performance and the number of subjects passed after two years of study. The results indicate that the performance in Mathematics I has a better predictive value than any other variable investigated. The performance in Mathematics I may therefore be used as part of an early warning system for dropping out and in determining the size and nature of the support structures needed. Mathematics performance during the first semester at TUT is a significant determinant of academic success for National Diploma students in engineering disciplines.