Despite a growing national need to develop capabilities in science, technology, engineering, and mathematics (STEM), many men and women who are considered talented in these areas during high school choose not to pursue STEM undergraduate majors. A purpose of the current study was to better understand factors that contribute to an individual's formal entry into the domain through the declaration of a STEM college major. Survey methodology was used to explore the perceptions of 360 Science Talent Search semifinalists and finalists from the years 1987 to 1989 and 1997 to 1999, and quantitative procedures were used to analyze the data. A majority (74.2%) of these students declared STEM majors and went on to graduate with STEM degrees. Belief in one's ability to achieve in STEM and the quality of students' academic experiences (level of challenge, hands-on nature, and adequacy of preparation for careers) were predictors of STEM majors in college. Reasons for attrition and implications for practice are discussed. (Contains 6 tables.)