Shoulder rotator cuff impingement syndrome is a common and disabling problem for the wheelchair athlete. In this study we investigated the role of shoulder strength imbalance as a factor for the development of this syndrome. Nineteen paraplegic male athletes underwent clinical and isokinetic examination of both shoulders with peak torque values measured in abduction, adduction, and internal and external rotation. Twenty athletic, able-bodied men without shoulder problems were tested as controls. Ten (26%) of the paraplegic athletes had rotator cuff impingement syndrome. The results of the isokinetic testing demonstrated that 1) the paraplegics' shoulders were stronger than the controls in all directions (P < 0.05); 2) the strength ratio of abduction: adduction was higher for paraplegic athletes (P < 0.05); 3) paraplegics' shoulders with rotator cuff impingement syndrome were weaker in adduction and external and internal rotation than the paraplegic athletes without impingement syndrome (P < 0.05); and 4) paraplegics' shoulders with rotator cuff impingement syndrome had higher abduction:adduction and abduction:internal rotation strength ratios than the shoulders of paraplegics without impingement syndrome (P < 0.05). We concluded that shoulder muscle imbalance, with comparative weakness of the humeral head depressors (rotators and adductors), may be a factor in the development and perpetuation of rotator cuff impingement syndrome in wheelchair athletes.