This study sought to understand school counselor advocacy for lesbian, gay, and bisexual (LGB) students using the theory of planned behavior (Ajzen, 2015). The authors analyzed data from a non-random sample of 398 school counselors in the United States. Participants completed demographic items and the Attitudes subscale of the Sexual Orientation Counselor Competency Scale (SOCCS-A), Advocacy Self-Efficacy Scale (ASES), Motivation to Comply Scale (MTCS), LGB Advocacy Intention Scale (LGBAIS), and LGB Advocacy Activity Scale (LGBAAS). School counselors' attitudes and advocacy self-efficacy significantly predicted LGB advocacy intention. Attitudes, self-efficacy, and LGB advocacy intention significantly predicted LGB advocacy activity. Findings related to motivation to comply were inconclusive, indicating that it did not influence any changes in school counselor LGB advocacy intention or activity. The authors call for more general and LGBT-specific advocacy, training, and research in schools and counselor education programs, and more school counselor involvement in sex education reform.