The proportion of young offenders in England and Wales describing themselves as Muslim has risen.
One in five males in young offender institutions (YOIs) identified themselves as Muslim in 2011/12, compared with 16% in 2010/11.
The director of the Prison Reform Trust, Juliet Lyon, said it was “a big increase” but the reasons were unclear.
The proportion of youths in custody from black and minority ethnic communities also rose from 39% to 42%.
Ms Lyon said: “It could simply be there are more young Muslim men at the moment in the general population than there were a couple of years ago, but equally – and I think it’s important that the Prison Service investigates this – it could be that more young people are going to prison and then either converting to the Muslim faith whilst they’re in prison or they’re reverting to the Muslim faith.”
The cause of the increase in Muslims in youth jails is not known