This paper examines the effects of group performance anxiety on the attrition of women and minorities from science, math, and engineering majors. While past research has relied primarily on the academic deficits and lower socioeconomic status of women and minorities to explain their absence from these fields, we focus on the impact of stereotype threat--the anxiety caused by the expectation of being judged based on a negative group stereotype. Using data from the National Longitudinal Survey of Freshmen, our findings indicate that minorities experience stereotype threat more strongly than whites, although women do not suffer from stereotype threat more than men. Our findings also reveal that stereotype threat has a significant positive effect on the likelihood of women, minorities, and surprisingly, white men leaving science, technology, engineering and math majors.