A 69-year-old woman was admitted to hospital due to abdominal pain. An enlarged spleen was detected and extirpated. Histological examination and FACS analysis could not clearly differentiate between a splenic marginal zone lymphoma and a mantle cell lymphoma. Using molecular cytogenetic techniques, a complex karyotype including a translocation between chromosome 11 and 14 consistent with a triple fusion between heavy chain immunoglobulin locus (IgH) and cyclin D1 (CCND1) was demonstrated. Overexpression of cyclin D1 was detected by immunostaining. Thus the diagnosis of a splenic blastoid mantle cell lymphoma could be established. In this report, various aspects of differential diagnosis of splenic lymphomas are discussed.