We present a case of a subdural osteoma. A 29-year-old female presented with a 3-year history of headaches. Computed tomography scan revealed a homogeneous high-density lesion isolated from the inner table of the frontal bone (a lucent dural line) in the right frontal convexity. Magnetic resonance imaging revealed an extra-axial lesion with a broad base without dural tail sign and punctate enhancement pattern characteristic of abundant adipose tissue. Upon surgical excision, we found a hard bony mass clearly demarcated from the dura. The mass displayed characteristics of an osteoma upon histological examination. The symptom was relieved after operation.