10-year old girl visited with left temporomandibular area pain and swelling that had developed 1 week ago. Sonogram showed a small sized low echoic finding in left temporomandibular joint area suggesting inflammatory lesion. Temporal bone CT and MRI revealed a bony defect around zygomatic process of left mastoid bone. After antibiotic therapy, her pain was subsided, but the swelling was persistent. Mastoidectomy around zygomatic process was performed to eradicate the lesion and large amount of pus was drained. After surgery, her pain and swelling disappeared. Histopathological study revealed the finding of inflamed granulomatous tissue with organized inflammatory exudate. She did not report any problem 2 month after surgery.