This study assessed the site-specific effects of long-term tennis playing on the bone mineral density (BMD) and content (BMC) of upper extremities in male Finnish top-level players using a dual energy x-ray absorptiometric (DXA) scanner. In players (n = 20), the BMDs and BMCs were significantly higher in each bone of the playing right extremity (p < 0.05-0.001), the side-to-side difference being largest in the humeral shaft (BMD + 25.4%, BMC + 28.7%) and proximal humerus (BMD + 14.4%, BMC + 20.5%), and smallest in the ulnar shaft (BMD + 3.1%, BMC + 7.5%) and distal ulna (BMD + 6.3%, BMC + 7.8%). In sex-, age-, weight-, and height-matched controls (n = 20), the right-to-left differences were small ranging from 0.0% to + 6.4% (average +3%). The number of training sessions per week was the only variable in muscle strength and training history assessment which showed, in several anatomic sites, a significant correlation with the relative bone mineral variables (r = 0.460-0.627, p < 0.05-0.001). In conclusion, long-term unilateral tennis activity had a clearly positive effect on the BMD and BMC of the bones of the playing extremity. The effect was very site-specific, being greatest in the humerus and smallest in the ulna. The effect was always greater in BMC than BMD indicating that the excess mineral was used not only for condensation of the bone tissue, but also for enlargement of bone dimensions.(ABSTRACT TRUNCATED AT 250 WORDS)