Rosai-Dorfman disease was originally described as sinus histiocytosis with massive lymphadenopathy.This rare benign disorder is characterized by the proliferation of non-Langerhans histiocytes that exhibit emperipolesis, S100+, CD68+, CD30+, CD1a- and Langerin-. The gene discussed is CD207; the disease is sinus histiocytosis with massive lymphadenopathy.