Sinus histiocytosis with massive lymphadenopathy is a benign pseudolymphomatous disease with distinctive microscopic features. Painless cervical adenopathy is the most characteristic clinical finding, although other node groups and extranodal sites may be involved. Of 200 patients in a case registry, 8 had neurologic symptoms. The lesions included vertebral canal and intracranial infiltrates and a destructive vertebral body lesion. Two patients had both cord compression and intracranial disease; one of them died after 10 years of disease. Seven patients were alive 1 to 15 years after disease onset.