The relative length of the second and fourth digits (2D:4D) is a putative marker 
for prenatal testosterone. Low 2D:4D has been reported to correlate with high 
performance in sport in general. Here, for the first time, we examine the 
relationship between 2D:4D and performance in elite rugby players. The 44 
players (28 forwards, 16 backs) were drawn from the Ospreys Rugby Union Club and 
44 age-matched controls. The measures of performance comprised age-adjusted 
number of international performances (caps) for Wales, a comparison of coaches' 
first-choice League team with others, and the number of tries scored by backs in 
club matches. Compared with controls, players were larger and had lower 2D:4D 
for the right and left hand. With regard to number of caps, players with low 
2D:4D in their right hand and low right 2D:4D compared with their left 
(right - left 2D:4D difference) had high numbers of caps. First-choice players 
did not differ significantly from second-choice players in their 2D:4D but they 
did have a lower right - left 2D:4D difference than second-choice players. Low 
right 2D:4D and low right - left 2D:4D difference were significantly linked with 
large numbers of tries. We conclude that low right 2D:4D and low right - left 
2D:4D difference are predictors of high rugby performance.