Sinus histiocytosis with massive lymphadenopathy (SHML) or Rosai-Dorfman disease is an unusual, benign, selflimited condition of unknown etiology which generally presents as massive bilateral cervical lymphadenopathy in children. It is differentiated from other childhood histiocytosis by its distinct character and should be kept in mind for differential diagnosis of neck mass in children because of the different treatment modalities. In this article a case of neck mass in a 10-month-old boy with diagnosis of SHML is presented. The clinical features, cytopathological characteristics of diagnosis and the treatment of disease are discussed and the literature is reviewed.