OBJECTIVES: To add to the area of triathlon research by providing much needed prevalence data on knee injury in triathletes. METHOD: An incidental "in field" sampling technique was used to interview 58 triathletes aged between 15 and 55 years about knee injury during a triathlon event. The sample comprised 46 men and 12 women. RESULTS: Most knee injuries occurred during the running event (72%) and affected the lateral side of the knee (38%). In all, 78% of the sample sought treatment from a healthcare professional. CONCLUSION: The study has provided much needed prevalence data on chronic knee injury in triathletes.