The authors present a case of a 4-year old boy with a quickly growing tumor of the jaw. The CT examination revealed a destructive tumor in the body of the mandible involving soft tissues. A diagnosis of eosinophilic granuloma of the mandible was confirmed by a biopsy of the tumor. Skeletal scintigraphy showed areas of increased and decreased radiotracer uptake. The fusion of CT and scintigraphy images showed that the "cold" focus corresponds with the osteolytic area and the "hot" focuses are larger than the areas of osseous reconstruction shown in CT. Conclusion: In cases of histiocytosis skeletal scintigraphy and CT are complementary methods that enable one to make an assessment of the extent of the disease.