Anthropogenic activities are increasingly linked to emerging diseases that cause mortality across many taxa. Human interference arising from ecotourism, in particular, can increase the stress levels of wild populations and promote the spread of disease. In Akumal Bay, Mexico, green sea turtles (Chelonia mydas) are increasingly infected with fibropapillomatosis (FP), an infectious disease associated with stress‐induced immunosuppression linked to high human density, which is particularly high in this area because of the increasing number of tourists visiting all year round. To examine whether FP might be associated with behavioural indicators of stress and varying levels of tourist pressure, the behaviour of turtles and the number of tourists were observed through 20‐minute focal sampling periods from May to August 2017. Disease presence and tourist pressure were related to several aspects of turtle behaviour, specifically feeding, resting, vertical movements (i.e. surfacing and diving), and evasive responses. Turtles that had visible FP engaged in fewer feeding periods, vertical movements, and evasive responses. Additionally, with increasing tourist pressure, all turtles spent less time engaging in vertical movements and had more evasive responses. These results suggest that the presence of FP affects green sea turtle behaviour, potentially increasing their exposure to tourists. Sick and healthy turtles appear to react differently to tourists, suggesting that FP changes behavioural responses to tourist pressure. Future management strategies should consider regulating tourist pressure on sick animals to reduce the incidence and progression of FP and other wildlife diseases by limiting access to critical habitats and enforcing code‐of‐conduct compliance from visiting tourists.