We report the cytogenetic findings on 31 cases of splenic lymphoma with villous lymphocytes (SLVL). TPA stimulated cells from peripheral blood (28 cases), spleen (two cases) and lymph node (one case) with SLVL have been analysed. A clonal chromosome abnormality was found in 27/31 patients (87%); this was identified as a simple abnormality in 12 cases and a complex one in 15. Four recurring abnormalities were seen: t(11;14)(q13;q32) in five patients, deletions or translocations involving 7q in seven patients, iso 17q in four patients and translocations involving 2p11 in four patients. The high frequency of clonal chromosome abnormalities in SLVL contrasts with the usually benign clinical course of this disease. Abnormalities found frequently in patients with chronic lymphocytic leukaemia (CLL) such as trisomy 12 and deletions or translocations involving 13q14 were each seen in only one patient. No case had the t(14;18) characteristic of follicular lymphoma. Our findings demonstrate the high frequency of clonal and often complex chromosome abnormalities in SLVL. Although a unique chromosome rearrangement has not been identified, a pattern of four recurrent abnormalities has emerged. Our results suggest that SLVL is distinct on cytogenetic grounds from B-CLL and follicular lymphoma but shows similarity with mantle cell lymphoma, lymphoplasmacytic lymphoma and B-PLL.