Primary splenic lymphoma (PSL) is extremely rare, accounting for less than 1% of all reported cases of extranodal lymphoma. A 62-year-old woman was referred to our hospital because of general fatigue. A heterogenous mass with irregular margins was detected in the spleen by abdominal computed tomographic scan, and Gallium scintigraphy demonstrated abnormal accumulation only in the spleen. Malignant lymphoma was strongly suspected on the basis of histologic findings from an ultrasonically guided needle biopsy. The final diagnosis was established by splenectomy as PSL of diffuse large B-cell type. After 6 courses of CHOP chemotherapy, the patient recovered and has been disease-free more than a year. Chromosomal analysis of her tumor cells detected t(3;14)(q27;q32), an abnormality not reported in cases of PSL to date. The rearrangement of BCL-6 was also observed. We discuss the possibility of BCL-6 involvement in Japanese cases of PSL, with reference to case reports dating back over the past decade.