Associations between youths' relationship profiles and mentoring outcomes were explored in the context of a national, randomized study of 1,139 youths (54% female) in geographically diverse Big Brothers Big Sisters school-based mentoring programs. The sample included youths in Grades 4-9 from diverse racial and ethnic backgrounds, the majority of whom were receiving free or reduced-price lunch. Latent profile analysis, a person-oriented approach, was used to identify 3 distinct relational profiles. Mentoring was found to have differential effects depending on youths' preintervention approach to relationships. In particular, youths who, at baseline, had satisfactory, but not particularly strong, relationships benefited more from mentoring than did youths with profiles characterized by either strongly positive or negative relationships. Implications for research and practice are discussed. (Contains 1 figure and 8 tables.)