Sinus histiocytosis is a newly recognized benign disease affecting mainly children and young adults and usually having a protracted clinical course that is relatively unaffected by therapy. This paper describes four additional patients who had orbital involvement initially and reviews the salient clinical and histopathologic features of this entity. The outstanding clinical feature is cervical lymphadenopathy. Associated findings include low-grade fever, anemia, leukocytosis, and elevated IgG levels. A small percentage of patients develop proptosis with palpable orbital tumors. Such patients may not have appreciable lymphadenopathy. Progressive proptosis may lead to exposure keratitis, corneal ulceration, endophthalmitis, and loss of the eye. Histopathologically, the lymph nodes and orbital mass show a proliferation of large histiocytes intermixed with a variable proportion of lymphocytes and plasma cells. Lymphocytes and occasionally other cells derived from the hematopoietic system are commonly seen within the cytoplasm of the histiocytes.