Introduction: Sinus histiocytosis with massive lymphadenopathy is an infrequent, self-resolving histoproliferative disorder of benign nature, also known as Rosai–Dorfman Disease. The typical manifestation of this disease includes bilateral, progressive cervical lymphadenopathy along with pyrexia. Laboratory manifestations consist of raised erythrocyte sedimentation rate, leukocytosis and hypergammaglobulinemia. Case report: An 8 year old female child presented with progressive, painful cervical and submandibular lymphadenopathy of three months duration. There was polymorphic leukocytosis and anemia along with raised Erythrocyte sedimentation rate and hypergammaglobulinemia. Fine Needle Aspiration cytology revealed sinus histiocytosis with massive lymphadenopathy, which was confirmed by the cervical lymph node biopsy. The histopathology revealed dilated sinuses filled with lympho plasma cells, large histiocytes and engulfed neutrophils (Emperipolesis). Conclusion: Massive, progressive bilateral cervical and sub mandibular lymphadenopathy, suggesting Sinus histiocytosis and massive lymphadenopathy-Rosai–Dorfman Disease. This was confirmed by Cytology, histopathology and immuno- histochemistry.