This paper studies the role of the judicial branch in the penal control of youth. It addresses the decisions of the Superior Appeal Court and the Appeal Court of the State of Rio Grande do Sul, regarding preventive detention (custody before sentence) of youth charged with criminal offenses.  Following the classification of the decisions, according to pre-established criteria, it finds that there are three major themes related to preventive detention of youth: prorogation of the legal term, detention before the decision becoming definitive and the reasoning for the decisions. This article investigates the reasons Courts use to decide whether or not preventive detention should be applied. After a new reduction of the empirical universe, guided by the observation of the collected data, the study focuses on the decisions related to drug trafficking, which places second in youth incarceration rates. The analysis finds that, despite some differences between the Courts, the discretion provided by the Child and Adolescent Act’s indeterminate language is used to widen the application of preventive detention. Also, in some cases, the legal provisions were given a flexible interpretation, to, once more, justify the increase of penal control.