The Big Five Inventory (BFI) measuring the 5-factor personality model was given to 440 science and engineering students in introductory physics classes at a large US university. Science and engineering students showed similar personality characteristics as would be expected from measurements of the general population, with women scoring significantly differently only on the neuroticism scale. The BFI facets had differential explanatory power for test average and course grade with the conscientiousness facet as the only significant treatment effect for course grade, but it was not significant for test average. High school GPA explained substantially different levels of variance in course grade for male and female students; these differences were reduced with the addition of BFI facets to the regression models.