We intended to compare the anthropometry of male and female Ironman triathletes with the anthropometry of male and female ultra-swimmers. Body mass, body mass index and body fat were lower in both male and female triathletes compared to swimmers. Body height and length of limbs were no different between the two groups. In the multi-variate analysis, in male triathletes, body mass (p=0.015) and percent body fat (p=0.0003) were related to race time; percent body fat was also related to the swim split (p=0.0036). In male swimmers, length of the arm was related to race time (p=0.0089). In female triathletes and swimmers, none of the investigated anthropometric variables showed an association with race time. We concluded that Ironman triathletes and ultra-swimmers were different regarding anthropometry and that different anthropometric variables were related to race time. We assume that other factors, such as training and equipment, as opposed to anthropometry, may better predict race time in male and female Ironman triathletes.