Background: Engineering programs have high attrition rates, and once in college, students are unlikely to migrate to engineering from other majors. Factors that influence retention must be assessed. Purpose: This study investigated the relationships of aptitude and personality traits in predicting retention for persisting students, those leaving in good standing, and those leaving in poor standing. Design/Method: Participants were entering first-year students from 2007 to 2010. Aptitude was assessed by the Assessment and LEarning in Knowledge Spaces (ALEKS) placement test as a measure of calculus readiness, Scholastic Aptitude Tests (math and verbal), and high school grade point average (GPA). Personality traits were assessed by the NEO Five-Factor Inventory and a measure of locus of control. A multinomial logistic regression was performed with students who persisted as the reference group. Results: Significant aptitude predictors for retention were high school GPA, SAT math, and ALEKS scores. Conscientiousness was the only significant personality factor. Conclusion: Math skills, especially calculus readiness, were strong predictors of retention. High school academic performance and Conscientiousness were also significant predictors. Application of these findings includes helping students with deficiencies, especially in calculus readiness, as well as fostering an environment that encourages conscientious academic behaviors.