We present a case of osteoid osteoma of the humerus diagnosed after it
presented clinically as impingement syndrome. Clinical and magnetic r
esonance imaging data supported impingement, but standard non-surgical
treatment did not provide complete pain relief. Subacromial injection
resolved the anterior shoulder pain and unmasked medial arm and axill
ary pain. Humerus X-rays revealed a lytic diaphyseal lesion, and en-bl
oc resection of the humeral mass diagnosed an osteoid osteoma, This ca
se is unusual in that only 1% of osteoid osteomas present in the humer
al shaft. The clinical features and presentation of impingement and os
teoid osteoma are discussed.