Organizations establish formal mentoring programs to advance personal and professional development, but not all relationships between mentors and protégés deliver these results. Based on the similarity-attraction paradigm, it is proposed that protégés receive more career and psychosocial support if mentors and protégés have similar personalities. A test of the model with data from a sample of 68 mentor–protégé dyads of a formal mentoring program showed, first, that career support is linked to mentor and protégé similarity in the personality trait openness to experience and, second, that psychosocial support for protégés is linked to mentor and protégé similarity in openness to experience and conscientiousness. It is concluded that matching mentors with protégés on two specific personality traits, openness to experience and conscientiousness, enhances the outcomes of mentoring relationships for protégés.