BACKGROUND: Marine turtles of all species are capable of being toxic. On 17 October 2010, health authorities in the Federated States of Micronesia were notified of the sudden death of three children and the sickening of approximately 20 other people on Murilo Atoll in Chuuk State. The illnesses were suspected to be the result of mass consumption of a hawksbill turtle (Eretmochelys imbricata). An investigation team was assembled to confirm the cause of the outbreak, describe the epidemiology of cases and provide recommendations for control. METHODS: We conducted chart reviews, interviewed key informants, collected samples for laboratory analysis, performed environmental investigations and conducted a cohort study. RESULTS: Four children and two adults died in the outbreak and 95 others were sickened; 84% of those who ate the turtle became ill (n = 101). The relative risk for developing illness after consuming the turtle was 11.1 (95% confidence inteval: 4.8–25.9); there was a dose-dependent relationship between amount of turtle meat consumed and risk of illness. Environmental and epidemiological investigations revealed no alternative explanation for the mass illness. Laboratory testing failed to identify a causative agent. CONCLUSION: We concluded that turtle poisoning (also called chelonitoxism) was the cause of the outbreak on Murilo. The range of illness described in this investigation is consistent with previously reported cases of chelonitoxism. This devastating incident highlights the dangers, particularly to children, of consuming turtle meat. Future incidents are certain to occur unless action is taken to alter turtle-eating behaviour in coastal communities throughout the world.