The ''histiocytes'' are a group of proliferative disorders of the mononuclear phagocyte system whose etiologies are basically unknown. The majority of childhood histiocytoses are expressions of excessive numbers of Langerhans cells, representing so-called Langerhans cell histiocytosis. Fifteen patients who were diagnosed with histiocytosis syndrome at the Pediatric Hematology and Oncology Department of Ege University Hospital between October 1986 and January 1995 were included in this study. The majority of the patients had Langerhans cell histiocytosis (LCH), and skeletal involvement was the most common manifestation. A good response to radiotherapy and chemotherapy was obtained by our patients with unifocal and multifocal involvement of LCH. Two patients with disseminated LCH died with progressive disease. In the patient with Rosai-Dorfman disease, a partial response was obtained with prednisone. The patient with malignant histiocytosis died during a relapse at the end of one year. Organ dysfunction and the patient's age are important factors affecting the outcome of the disease.