In 1985 the maximum age for juvenile court jurisdiction under the Young Offenders Act became 18. Except for Quebec and Manitoba, there will be a major increase in the number of juveniles handled by the juvenile justice system. Since more of these juveniles will be labeled serious offenders, there is concern over the system's capacity for institutionalizing juveniles deemed dangerous. In France the juvenile justice system must address problems with complexity similar to those faced in Canada, yet the French use closed custody for juveniles less often than some North American jurisdictions. Juvenile justice in Val-de-Marne, on the outskirts of Paris, and the Province of Alberta are compared. The logic of French judges differs from that of their North American counterparts in that they reserve closed custody for juveniles who have committed crimes, excluding custody for juveniles who have only violated administrative decisions. North American judges, on the other hand, use closed custody for juveniles who do not comply with rules or decisions. The study considers whether as juvenile justice systems become more legalistic, there may also be a greater use of closed custody. 4 notes and 21 references. (Author abstract modified)