BACKGROUND We report three cases of sinus histiocytosis, a rare disease of unknown aetiology with massive lymphadenopathy (SHML), also known as Rosai-Dorfman (RD) disease, in a paediatric population. This proliferative histiocytic disorder is defined by histological and immunohistochemical (IHC) characteristics and can manifest as nodal involvement with variable enlargement of the lymph nodes (two cases) and extranodal manifestations involving skin and larynx involvement (one case). One patient had hypergammaglobulinemia. The morphological investigation revealed that all lymph nodes showed hyperplasia of sinuses with abundant histiocytic cell with intracytoplasmic lymphocytes. Skin and larynx biopsies showed a histiocyte and lymphocyte infiltrate with similar characteristics. An ultrastructural study was carried out on material from one patient. In the IHC study, SHML cells expressed phagocytic markers such as CD68 and S100, but markers for Langerhan's (CD1a) or dendritic cells (DRC, CD23 and CNA42) were absent. Two patients had a complete remission after surgical excision and no other treatment, but the third patient was treated with radiotherapy after a relapse with obstruction of the upper airway. CONCLUSIONS This disorder must be considered in the differential diagnosis of young patients who exhibit massive or multiple lymphadenopathies, especially when involvement of the cervical area occurs. Due to the good outcome of the disease, a conservative approach is justified.