OBJECTIVE To study the clinicopathologic features of Rosai-Dorfman disease (RDD), expression of various antigens, human herpes virus type 8 (HHV8), human papillomavirus (HPV)-DNA and Epstein-Barr virus (EBV)-mRNA, and compare the findings with those in the literature. METHODS The clinicopathologic findings of 16 Rosai-Dorfman disease cases were retrospectively reviewed. Immunohistochemical study for S-100 protein, CD68 (PG-M1), CD163, CD21, CD1a, CD20, CD45RO, CD4, CD8, M-CSF and HHV8 was carried out in 9 of the 16 cases. In-situ hybridization for EBV-mRNA and HPV-DNA was also performed. RESULTS The male-to-female ratio of the patients was 4.33:1. Amongst the 16 cases studied, 62.5% (10/16) presented nodal RDD, with cervical lymph node predominantly involved. Half of these cases had affected lymph nodes in more than one anatomic site. Extranodal RDD represented 37.5% (6/16) of the cases. The relapse rate of extranodal RDD was higher than that of nodal RDD. Histologically, nodal RDD was characterized by dilated sinuses filled with large polygonal histiocytes which contained lymphocytes and plasma cells. For extranodal lesions, various degrees of stromal fibrosis were seen in association with mixed inflammatory cells (especially plasma cells). The large polygonal histiocytes varied in number and were distributed in clusters or patches. Immunohistochemical study showed that the abnormal histiocytes were strongly positive for S-100 protein. They also expressed CD68, CD163 and M-CSF, but were negative for CD1a, CD21 and HHV8. The lymphocytes in cytoplasm of these histiocytes were positive for both T and B cell markers (with T cell predominance, including a mixture of CD4- and CD8-positive cells). HPV-DNA and EBV-mRNA were not detected by in-situ hybridization. To date, 62 cases of RDD have been reported in mainland China, including 34 cases of nodal RDD and 18 cases of extranodal RDD. The remaining 10 cases involved both lymph nodes and extranodal sites. Compared with overseas reports, RDD occurring in China tended to affect older patients and with slight male predilection. CONCLUSIONS Rosai-Dorfman disease is relatively rare in China. Pathologic diagnosis of extranodal RDD may be difficult. The demographic data of RDD in China, including age and sex of patients, are different from those in the literature.