A 9-year-old boy presented a painful right painful parietal mass that rapidly enlarged within a month. He had no other symptom of infection or malignancy. Laboratory findings were normal. Plain skull X ray demonstrated a "punched-out" lesion in the right parietal bone. Magnetic resonance (MR) imaging revealed a 4 x 4 x 3 cm mass centered in the right parietal bone which was enhanced after administration of a contrast material. In addition, as well as the mass region, the pericranial soft tissue was densely enhanced. The parietal bone mass was soft and successfully removed. Histological examination disclosed Langerhans cell histiocytosis (LCH) infiltrating the temporal muscle. MR imaging is useful for diagnosis of LCH of the skull with soft tissue involvement.