Findings from the study suggest that youth who have a high number of pre-existing vulnerabilities and who experience high prison stress at entry into custody are more likely to experience adjustment difficulties at entry into custody. In addition the study suggests that as youth spend more time in custody, their levels of pre-existing vulnerabilities remain important. In addition, however, the findings suggest that the level of support that youths have and their level of fear also become important in understanding their adjustment to custody. Hence youth who have high levels of preexisting difficulties, who feel they have little support in the institution and who are relatively fearful are likely to experience adjustment difficulties as they spend more time in a facility.This dissertation describes a short-term longitudinal study of the experiences of youths in custody. It examines the stress and adjustment to custody of youths in a number of custodial facilities in Southern Ontario. It addresses key issues raised by the literature on adult adjustment to prison and by the psychological developmental literature. More specifically, it explores whether pre-existing vulnerabilities (and an importation model of adjustment) or institutional vulnerabilities (and a deprivation model of adjustment) are separate predictors of custodial adjustment. In addition it investigates whether pre-existing vulnerabilities and institutional variables interact in their effects on adjustment.The study argues that staff may play a vital role in the adjustment of youth in custody by creating a climate amongst youth in custody that will foster positive social interactions, a sense of stability, and a secure environment.