Background. Inflammatory pseudotumor or inflammatory myofibroblastic tumor is a benign, tumor forming proliferation of myofibroblasts with a potential for recurrence and persistent local growth, in some respects similar to fibromatosis. The lesion does not metastasize except exceedingly rarely. Though inflammatory pseudotumor is not a malignant lesion, it may occasionally behave aggressively, like fibromatosis or fibrosarcoma, and threatens patient’s life.Patients and methods. Patient D. E., born in 1974, in the second month of pregnancy, was admitted to our Clinic in 1996 because of the protrusion of the left eye. She has often had evening headaches for the last 5 years. She has previously been treated for epistaxis. CT showed a tumorous formation in the ethmoidal labyrinth, which grew into adjacent structures, destroyed the neighboring bones and extended into extradural space of cranial cavity.The patient was operated upon at the ENT clinic where a tumor of a »woman’s fist« size was excised. It showed expansive, non-infiltrative growth. Microscopically, it was an inflammatory pseudotumor. For one year after the operation the patient was in good health, without protrusion. After that period, she had repeated recurrences, reoperations, she was irradiated and received chemotherapy. In spite of all treatment, the tumor locally progressed and the patient died in December 2000. Conclusions. Although repeated histopathologic examinations showed a benign inflammatory pseudotumor, because of the proximity of vital structures the course of disease was malignant just like in a malignant neoplasm.