Four cases of different types of orbital, benign and malignant histiocytosis syndromes are presented to demonstrate the diagnostic presentation, medical evaluation, and therapy of these diseases with orbital involvement. Newer concepts have altered our understanding of the pathophysiology of histiocytic syndromes. An abnormality of Langerhans' cells and the T-cell suppressor population appears to be important in the development of histiocytosis. It is important for the ophthalmologist to be aware that histiocytic lesions of the orbit may be an indication of widespread and at times life-threatening disease.