Objectives: This study assessed potential differences between girls and boys in the prevalence rates of cannabis use, sociodemographic factors, and beliefs about cannabis use.Methods: 1,896 Andalusian adolescents aged 14–18 participated in an online survey based on the I-Change model. The survey assessed their beliefs about cannabis use, including attitudes, social influences, self-efficacy, action planning, and intention to use. Multivariate analyses of variance were then conducted to examine potential gender differences in these beliefs, while controlling for last month’s cannabis use.Results: Significantly more boys used cannabis in the last month, had boyfriends/girlfriends, and had more pocket money compared to girls. Additionally, girls – in comparison to boys - were more convinced of the disadvantages of cannabis use, but were also more convinced of some of the advantages (such as freedom from boredom, and medicinal use), reported having less favorable social norms for cannabis use, had more female best friends using cannabis, and felt pressure to use cannabis from their female peers.Conclusion: These findings highlight the need for cannabis prevention programs to consider gender differences in beliefs about cannabis use. Programs should not only address general risk factors for cannabis use but also evaluate if their interventions effectively target beliefs that are particularly important for girls and boys.