Triathletes and ironman triathletes engage in an extremely intense sport that involves hours of considerable pain, as well as physical and psychological stress, every day. The basic pain modulation properties of these athletes has not been established and therefore it is not clear whether they present with unique features that enable them to engage in such efforts. The aim was to investigate the existence of possible alterations in pain perception and modulation of triathletes, as well as possible underlying factors. Participants were 19 triathletes and 17 non-athletes who underwent measurement of pain threshold, pain tolerance, suprathreshold perceived pain intensity, temporal summation of pain, and conditioned pain modulation (CPM). Participants also completed the fear of pain and the pain catastrophizing questionnaires, and rated the amount of perceived stress. Triathletes exhibited higher pain tolerance (P < .0001), lower pain ratings (P < .001), and lower fear of pain values (P < .05) than controls. The magnitude of CPM was significantly greater in triathletes (P < .05), and negatively correlated with fear of pain (P < .05) and with perceived mental stress during training and competition (P < .05). The results suggest that triathletes exhibit greater pain tolerance and more efficient pain modulation than controls, which may underlie their perseverance in extreme physical efforts and pain during training/competitions. This capability may be enhanced or mediated by psychological factors, enabling better coping with fear of pain and mental stress.