Over 3 months, a healthy man developed prominent systemic symptoms that defied investigation. Physical examination was noncontributory, and extensive studies revealed only a marked acute-phase response associated with increased serum IL-6 levels. A whole body Gallium-67 scan was crucial in diagnosis, directing attention to high uptake in the left paraspinal and psoas muscles. Open surgical excision biopsy was performed, guided by intraoperative use of a gamma-probe. Removed tissue was diagnosed as diffuse, large B-cell non-Hodgkin lymphoma of muscle (stage IE), a rare extranodal lymphoma. Cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) therapy was given, and the patient became asymptomatic with normal blood tests and was thought to be in remission. However, a repeat Gallium-67 scan revealed recurrent multifocal disease and salvage chemotherapy was instituted. A 47,XXY karyotype (Klinefelter syndrome) was later identified, possibly associated with the lymphoma.