Five studies on the development of the Lesbian, Gay, and Bisexual Affirmative Counseling Self-Efficacy Inventory (LGB-CSI) were conducted. Exploratory and confirmatory factor analyses of an initial pool of 64 items yielded 5 factors that assess counselor self-efficacy to perform lesbian, gay, and bisexual (LGB) affirmative counseling behaviors (Application of Knowledge, Advocacy Skills, Self-Awareness, Relationship, and Assessment Skills). The LGB-CSI evidenced high internal consistency; however, low test-retest reliability was found over a 2-week period. Convergent validity was supported by correlations with measures of general counseling self-efficacy and attitudes toward LGB individuals. Discriminant validity was evidenced by an absence of relations between the LGB-CSI and measures of social desirability, self-deceptive positivity, and impression management. Construct validity was supported by findings indicating varying levels of self-efficacy commensurate with status in the field. Recommendations for training interventions are discussed.