It is widely assumed that placing offenders (juvenile or adult) in custody acts as a deterrent to further offending. The present study was designed to see whether juvenile offenders who receive a detention sentence are less likely to re-offend, controlling for other factors, than juvenile offenders given some other form of sentence. Two groups of offenders (152 given an detention sentence, 243 given a non-custodial sentence) were interviewed at length about their family life, school performance, association with delinquent peers and substance abuse. They were then followed up to determine what proportion in each group was reconvicted of a further offence. Cox regression was used to model time to reconviction. The study found no significant difference between juveniles given a custodial penalty and those given a non-custodial penalty in the likelihood of reconviction, even after controlling for factors that differ between the two groups.