Abstract: Rosai-Dorfman disease, or sinus histiocytosis, first described in 1969, is a benign systemic disorder of histiocytes of unknown etiology characterized by massive lymphadenopathy. It predominantly involves the head and neck region, and is often associated with extranodal involvement. Patient presented to pulmonology with history of sudden onset dyspnea. Clinically and radiologically, the lungs were normal. D-dimer test was noncontributory. As the patient had a family history of lymphedema, lymphoscintigraphy was sought. We report the detection of an unsuspected case of Rosai-Dorfman disease by lower limb lymphoscintigraphy.