OBJECTIVE: To explain rising rates of sexually transmitted infections it is necessary to monitor trends among high risk groups, such as youth. Surveillance of risk behaviours and testing among a variety of populations in different settings is required. We monitored self-reported sexual behaviour among music festival attendees. METHODS: Cross-sectional studies of young people’s behaviour were conducted annually at a music festival between 2005 and 2008 using self-administered questionnaires. Logistic regression, adjusted for age and gender, determined trends in risk behaviours. RESULTS: More than 5,000 questionnaires were completed. The proportion reporting multiple sexual partners in the past year remained stable from 2005 to 2008 and condom use with these partners increased. Reporting a new sexual partner in the past three months decreased, while condom use with new partners increased. Reporting a casual sexual partner increased and condom use with casual partners remained stable. Reporting a recent STI test increased from 23% in 2006 to 32% in 2008. CONCLUSIONS AND IMPLICATIONS: Despite increases in STI notifications, most risk behaviours are decreasing in this group, possibly as a function of increased STI testing. Music festivals are a useful setting for monitoring behaviour trends within a sub-population of young people at relatively high risk of STIs.