This paper examines the various risk factors that are considered in the current risk assessments used with sex offenders, and the strengths and weaknesses of each. In addition, particular attention is given to the assessments that are currently employed within the prison and probation services. Static instruments, dynamic instruments and combined approaches are evaluated, as are clinical assessments of risk. In particular, the now commonly used joint Prison-Probation Offender Assessment System risk prediction instrument (OASys) is considered, with an evaluation of the relevance of the factors included in making an assessment of risk and whether this is supported by research into recidivism amongst sex offenders. Copyright © 2006 John Wiley & Sons, Ltd.