This study examined the reciprocal longitudinal relations between homophobic attitudes and homophobic bullying at school. Furthermore, the study also assessed the roles of exposure to homophobic bullying at school, homophobic language at home, and previous social interaction with individuals who identify as lesbian, gay, bisexual, or transgender (LGBT) as predictors both of homophobic attitudes and bullying. A total of 791 adolescents (56.38% boys; ages 12-17; M = 13.96, SD = 1.18) completed measures of homophobic attitudes, carrying out homophobic bullying, exposure to homophobic bullying at school, exposure to homophobic language at home, and social interaction with individuals who identify as LGBT. The results indicated that homophobic attitudes at Time 1 (T1) predicted homophobic bullying at Time 2 (T2), and homophobic bullying at T1 predicted homophobic attitudes at T2. Moreover, exposure to homophobic bullying at school at T1 predicted homophobic bullying at T2. Some gender differences emerged in the relations between the variables, which suggests that prevention and intervention in homophobic bullying should be tailored to fit different individual needs.