We report a very rare case of a chondromyxoid fibroma of the mastoid portion of the temporal bone in a 38-year-old woman who presented with left-sided hearing loss. Magnetic resonance imaging identified an expansile mass in the left mastoid bone with a heterogeneous hyperintense signal on T2-weighted imaging and peripheral enhancement. Subsequent positron emission tomography/computed tomography identified erosive bony changes associated with hypermetabolism. The patient underwent an infratemporal fossa resection with a suboccipital craniectomy/cranioplasty. We briefly review the aspects of this case, including a discussion of the differential diagnosis and the correlation between histologic and imaging findings.