There have been marked changes in methamphetamine use over the past decade as more potent forms of the drug have become increasingly available, particularly crystalline methamphetamine. A major concern of stronger potency methamphetamine is the increased potential for harm, such as psychotic symptoms and violent behaviour. Little is currently known about what effects methamphetamine use has on violent behaviour. This research was undertaken to improve understanding of the association between methamphetamine use and violent victimisation and offending. Information was gathered concerning prevalence, type of offence, circumstances surrounding victimisation and offending, and the predictors of violent behaviour. A sample of 400 regular methamphetamine and heroin users from the greater Sydney region were interviewed face-to-face regarding their lifetime and most recent experiences of violent victimisation and offending. Participants in the study were recruited through advertisements placed in needle and syringe programs (NSPs), therapeutic communities, street press publications, and word of mouth. Key findings were that violent victimisation, although almost universal, was not associated with methamphetamine use, whereas violent offending, also highly prevalent, was associated with its use. Despite high rates of victimisation and offending, perceived risks of becoming and offender or victim in the following 12 months were low. (Executive summary, edited)