The purpose of this study was to explore the personal stories of men who selected careers in science, technology, engineering, or mathematics (STEM) to better understand the ways in which their self-efficacy beliefs were created and subsequently influenced their academic and career choices. Analysis of 10 narratives revealed that mastery experience was the primary source of the men's self-efficacy beliefs. These results are compared to those from Zeldin and Pajares' earlier study involving women in STEM careers. For women, social persuasions and vicarious experiences were the primary sources of self-efficacy beliefs. Together, these findings suggest that different sources are predominant in the creation and development of the self-efficacy beliefs of men and women who pursue STEM careers. The self-efficacy beliefs of men in these male-dominated domains are created primarily as a result of the interpretations they make of their ongoing achievements and successes. Women, on the other hand, rely on relational episodes in their lives to create and buttress the confidence that they can succeed in male-dominated domains. Findings were consistent with the theoretical tenets of A. Bandura's social cognitive theory. (Contains 1 table.)