Using an experimental design with a sample of African-American high school students (n=94), this study examines the determinants of students' initial trust beliefs about adult mentors. Consistent with the model of initial trust formation, results indicate that both structural assurance beliefs and youth dispositions toward trust were positive, significant predictors of the belief in an adult mentor's benevolence, honesty, competence, and predictability. Mentor selection procedures were not related to any of the trust beliefs. Ethnic identity of the student was found to moderate the relation between two of these beliefs (competence and predictability) with racial similarity of the mentor and student. Contrary to expectations, African-American students with low ethnic identity believed that a White adult mentor would be more competent and predictable than students with high ethnic identity. Implications for work-based, adult-youth mentoring programs and future research are discussed.