Alcohol abuse and truancy are two widespread problems among the adolescent Spanish population. Given the negative consequences of both behaviours for human capital acquiring and their origin in adolescence, our study lies in analysing the relationship between these risk behaviours. From a methodological point of view, our contribution consists of considering unobserved factors that influence both alcohol abuse and truancy, that is to say, to test if there are individual or social factors that orient the adolescent to take both decisions. Given the nature of the data, we consider this relation by using a bivariate negative binomial model, which is estimated for a representative sample of the school population in Spain in 1996, 1998 and 2000. The results confirm the existence of these unobserved factors underlying the decisions to drink alcohol in excess and to play truant. The results also reveal the importance of the family environment in the truant-behaviour of the adolescent, as well as the usefulness of being a member of a social association and information campaigns about drugs in the reduction of alcohol abuse among adolescents.