During the outdoor tennis season of 1984 a prospective injury registration was done in 104 randomly chosen elite tennis players, of whom 86% could be followed. We found 46 injuries: an incidence of 2.3 injuries/player/1000 tennis hours. Men were more frequently injured than women. The prevalence was 0.3 injury/player. Upper extremity injuries were most frequent - 45.7% (21/46). Shoulder injuries were the single most frequent injury - 17% (8/46). The pathophysiology was overuse in 67% (28/42), strains in 14% (6/42), sprains in 17% (7/42), fractures in 2% (1/42), and blisters in 5% (2/42). Players using conventional rackets had more injuries to the upper extremity compared with players using mid/oversized rackets, though the difference was nonsignificant. The importance of impact forces from the tennis stroke in the mechanism of upper extremity injuries is discussed.