Marijuana use during adolescence may result in altered neurocognitive functioning; therefore, preventing or delaying the onset of marijuana use is a public health concern. Parenting styles have been consistently identified as influential risk factors for adolescent drug use. However, most relevant studies have focused on non-Latin American populations. This cross-sectional study aimed to determine the influence of parenting styles on the reasons for Costa Rican adolescents’ willingness to use marijuana using Structural Equation Models. 728 urban and rural adolescents (aged 13–18) participated in the study. Mothers and fathers rated as having an authoritative style were negatively related to the willingness to use marijuana (β = −0.18 and β = −0.13, respectively, p < 0.05), while mothers and fathers rated as having an authoritarian style were positively associated with this outcome (β = 0.13, β = 0.12, respectively, p < 0.01). Mothers rated as having a permissive style showed a positive association too (β = 0.13, p < 0.01). An authoritative style in both parents was negatively associated with the reasons for willingness to use marijuana: emotion regulation, social approval and fun, and perceived access to marijuana. Meanwhile, an authoritarian style presented positive and significant associations. Mothers rated as having a permissive style were positively related to emotion regulation (β = 0.11, p < 0.05), and social approval and fun (β = 0.09, p < 0.05). Reasons to use marijuana vary according to parenting styles, sociocultural context and same-sex parent/child dyads (mother/daughter, father/son). Hence, a careful examination of the relationships between these variables in various adolescent subpopulations will be a critical step in developing practical, culturally tailored adolescent health promotion interventions.