Abstract Sinus histiocytosis with massive lymphadenopathy (SHML), also called Rosai-Dorfman disease, is a rare entity. Its etiology and pathogenesis are still essentially unclear. The histologic hallmark of this disease is proliferation of distinctive histiocytes within lymph node sinuses and in extranodal sites. Approximately 23% of patients with SHML, documented in the SHML Registry, presented with disease primarily in extranodal sites, and very few cases of SHML (<1%) involving the gastrointestinal system have been described in the literature. We report an unusual case of primary pancreatic SHML with infiltration of the process into peripancreatic, perinephric, and perisplenic adipose tissue, simulating malignancy.