A 66-year-old man with a 6-month history of sweating at night, generalized lymphadenopathy, hepatosplenomegaly, and paraproteinemia was diagnosed to have a Stage IV mantle zone lymphoma (MZL), which behaved aggressively. The neoplasm rapidly disseminated to extranodal sites--the skin, lungs, pleural cavity, and the central nervous system. The neoplasm did not respond to initial double-agent chemotherapy, but it did partially respond to multi-agent chemotherapy. In addition, the neoplasm had histopathologic features not reported previously in MZL--vascular invasion, massive extranodal infiltration, high mitotic count, and convoluted nuclei.