Group of disorders which feature accumulations of active HISTIOCYTES and LYMPHOCYTES, but where the histiocytes are not LANGERHANS CELLS. The group includes HEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS; SINUS HISTIOCYTOSIS; xanthogranuloma; reticulohistiocytoma; juvenile XANTHOGRANULOMA; xanthoma disseminatum; as well as the lipid storage diseases (SEA-BLUE HISTIOCYTE SYNDROME; and NIEMANN-PICK DISEASES).