Rosai-Dorfman disease (RDD) or Sinus histiocytosis with massive lymphadenopathy is a rare and benign histiocytic proliferative disorder first described by Juan Rosai and Ronald Dorfman in 1969, whose etiology remains unknown. Since then, many cases were reported in the literature. The disease primarily involves the lymph nodes, and is characterized by painless, bilateral cervical lymphadenopathy accompanied by fever, night sweats, malaise and weight loss, reason why many patients are clinically misdiagnosed as malignant lymphoma. In some cases, extranodal involvement may be present. Leukocytosis, elevated erythrocyte sedimentation rate, and hypergamaglobulinemia are often present. The authors report a case of a 52-year-old female patient admitted to the hospital with the diagnosis of pneumonia and progressed to multiple organs failure and death. During the hospitalization an attempt to diagnose a lymphoproliferative disease trough an axillary lymph node biopsy was disappointing. The autopsy was crucial for the diagnosis, illustrating a severe and unusual presentation of Rosai-Dorfman disease.