Objective: As empirical evidence for the effectiveness of LGB-affirmative psychotherapy emerges, the question of whether some clients may derive greater benefit than others becomes important. The current study investigated whether internalized homonegativity (IH), both explicit and implicit, moderated the efficacy of a cognitive– behavioral intervention designed to improve the mental and sexual health of young gay and bisexual men through facilitating minority stress coping. Method: At baseline, young gay and bisexual men (n = 54) experiencing symptoms of depression and anxiety completed measures of explicit and implicit IH. Participants also completed self-reports of mental health and an interviewer-based assessment of past-90-day risk behavior before and after treatment in a 10-session individual LGB-affirmative intervention. Results: Moderation analyses showed that participants higher in implicit IH experienced greater reductions in depression (b = −2.99, p = .031, 95% confidence interval [CI] [−5.69, −0.29]), anxiety (b = −3.56, p = .014, 95% CI [−6.35, −0.76]), and past-90-day condomless anal sex with casual partners (b = −1.29, p = .028, 95% CI [−2.44, −0.14]). Participants higher in explicit IH experienced greater reductions in past-90-day heavy drinking (b = −0.42, p = .003, 95% CI [−0.69, −0.15]). Conclusions: These findings indicate that greater gains from LGB-affirmative psychotherapy were observed in gay and bisexual men who were higher in IH, particularly when measured implicitly. As the first study that examines factors moderating the efficacy of LGB-affirmative psychotherapy, the present research has important implications for intervention development and highlights the value of incorporating implicit measures into clinical work.