Previous studies of the characteristics of juvenile sex offending have been restricted to clinical samples (with convicted offenders undergoing treatment or assessment), which have several inherent limitations. To overcome these limitations victim allegations made to the London Metropolitan Police, UK, in 2001, of sexual assault by juvenile stranger perpetrators were sampled. The study aimed to determine more accurately the alleged nature of sex offending by this type of juvenile offender (aged less than 18 years) and to determine what factors were associated with the most serious cases of this type of aggressive behaviour. The most common offence characteristics were identified, and relationships between suspect and offence/victim characteristics were statistically tested. Offence seriousness, as indicated by physical violence and the occurrence of penetration, was significantly associated with an assault by a team of offenders, a young victim, and older juvenile offenders. The potential for predicting offender characteristics from offence characteristics was examined. Estimated offender age was significantly predicted by the absence/presence of penetration. An older juvenile offender was predicted by a penetrative attack. Aggr.A recent study by La˚ngstro¨m [2002] identified a stranger victim-suspect relationship, (where the victim was previously a stranger to the suspect), as a risk factor for sexual recidivism for a sample of Swedish juvenile sex offenders aged 15-20. Sex offences committed by stranger offenders are also the most difficult for the police to investigate, as the police often possess only scant information about the offender from a distressed victim. It would therefore be expected that juvenile sex offenders who commit offences against previously unknown victims would have been the subject of extensive research attention. This, however, has not been the case, as will be demonstrated.Past studies have shown juveniles to be responsible for a substantial proportion of sexual assaults, as indicated by a figure of approximately 19% reported by East and Campbell [1999] and a figure of 20% following a review by Davis and Leitenberg [1987]. Studies have shown