Diffuse plane xanthomatosis associated with haematologic disorder and solid tumor. Findings of an autopsy. Diffuse plane xanthomatosis is an uncommon subtype of non-Langerhans histiocytosis. We report a case of a 78 year-old woman with a history of monoclonal gammopathy of undetermined significance and diffuse plane xanthomatosis since 1995. She consulted for malaise and died four days after admission. Autopsy was requested. Findings were diffuse plane xanthomatosis with extensive involvement of internal organs, lymphoplasmacytic lymphoma and cecal adenocarcinoma. Final event was acute bronchopneumonia. This entity is a subtype of histiocytosis. It affects skin and involves mucous membranes in 40% of the cases. Extracutaneous extension has been reported. It is usually associated with haematologic disorders. In this case, the patient had a lymphoplasmacytic lymphoma and colonic adenocarcinoma. We highlight the importance of recognition its association with monoclonal gammopathies and solid tumors in order to make a proper follow up of patients.