A case of eosinophilic granuloma of the soft tissue arising in the palate of a 65-year-old man is reported. It was an elastic hard lesion measuring about 10mm in diameter. The lesion was removed under a clinical diagnosis of fibroma. Histologically, the lesion was diagnosed as an eosinophilic granuloma of the soft tissue.
Ultrastructurally, viruses similar to the herpes virus group, with a diameter of 100nm, were observed in the cytoplasm of histiocytes. These cells were positive for HSV (Herpes Simplex Virus)-Type I antibody on immunostaining. The findings indicate that the lesion was caused by Type I allergy due to HSV Type I infection.