Two patients with osteoid osteomas were evaluated with magnetic resonance imaging at 1.5 T using both conventional spin-echo (SE) and short TI inversion-recovery (STIR) sequences. On plain films the classic findings of a radiolucent nidus with a dense surrounding reactive zone of sclerosis were absent. The diagnosis was suspected on observing the presence of marked marrow oedema in the involved bone. Conventional SE images were unimpressive in detecting the bone marrow changes. Increased signal intensity indicating bone marrow oedema was striking on the STIR images and facilitated diagnosis. In cases of suspected osteoid osteoma which do not demonstrate the classic radiologic features, adding the STIR sequence to conventional SE magnetic resonance sequences to enhance detection of bone marrow change is recommended.