Osteoid osteoma is a relatively uncommon osteoblastic lesion of the bone that accounts for approximately 10% of all benign bone tumors and occurs predominantly in children and young adults, with a male-to-female ratio of 3:1 [1, 2]. More than half of osteoid osteomas occur in the femur and tibia, and the proximal femur is by far the most common location [2]. Its incidence in the small bones of the foot ranges from 2% to 11%, with the talus being the most common site of pedal involvement [2, 3]. No case specifically involving the fibular sesamoid has been reported in the literature. Except for its location, this case presents a classic history of OO, occurring in a 19-year-old woman and producing nighttime pain, relieved to some extent by salicylates. The classic presentation is a single small (<1.5 cm) round or oval lytic focus, which may contain a variable amount of ossification with a zone of reactive sclerosis [4]. The radiographic appearance of OO may be classified according to its location into cortical, cancellous, and subperiostal regions of bone [1, 5–7]. Typically, the tumor is cortical , comprising a small area of radiolucency less than 1 cm in diameter, subcortically placed, and associated with dense adjacent bone sclerosis and periostal reaction. The cancellous variety of OO displays less radiographic sclerosis than does the cortical type. The cancellous and subperiostal varieties have been reported to be more prevalent in the small bones of the hand and foot [7]. In our case there was a radiolucent nidus surrounded by an illdefined sclerotic rim, with central calcification as in the cancellous subtype. In patients with OO computed tomography demonstrates the radiolucent nidus with a smooth inner surface, and, in some cases, a radiodense center can be visualized, as in our case. This central calcification is suggested to represent the osteoblastic center of the lesion [8]. Bone scanning almost always produces positive findings and is valuable when plain radiographs are equivocal. A typical ‘hot spot’ is shown, due to intense radionuclide uptake by the lesion, as in our case [9]. The histopathologic appearance of the nidus may vary, depending on the maturity of the lesion [2]. The pathologic appearance of the nidus is of a small, round, mass of tissue which can be either soft or sclerotic, red, and surrounded by normal or sclerotic bone. Microscopic Skeletal Radiol (2009) 38:831–832 DOI 10.1007/s00256-009-0711-0