We investigated the association between skinfold thickness and race performance in male and female Ironman triathletes. Skinfold thicknesses at 8 sites and percent body fat were correlated to total race time including the split times for the 3 sub disciplines, for 27 male and 16 female Ironman athletes. In the males, percent body fat (r=0.76; p<0.0001), the sum of upper body skinfolds (r=0.75; p<0.0001) and the sum of all 8 skinfolds (r=0.71; p<0.0001) were related to total race time. Percent body fat (r=-0.67; p<0.001), the sum of upper body skinfolds (r=-0.63, p=0.0004) and the sum of all 8 skinfolds (r=-0.59; p<0.001) were also associated with speed in cycling during the race. In the females, none of the skinfold thicknesses showed an association with total race time, average weekly training volume or speed in the sub disciplines in the race. The results of this study indicate that low skinfold thicknesses of the upper body are related to race performance in male Ironman triathletes, but not in females.