The clinical, cytogenetic and molecular features of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), a disease previously considered to be rare in Asia, were examined in consecutive series of 70 cases diagnosed by our laboratory over a 30-month period. Clonal abnormalities were observed in 80% of CLL/SLL cases using a combination of conventional cytogenetic and fluorescence in situ hybridization (FISH) analysis. Those involving 14q32/IGH were the most frequent (24 cases), followed by trisomy 12 and 11q abnormalities. IgV(H) gene usage was non-random with over-representation of V(H)4-34, V(H)3-23 and a previously unreported increase in V(H)3-48 gene use. Somatic hypermutation (SHM) of IgV(H) germline sequences was observed in 56.5% of cases with stereotyped patterns of SHM observed in V(H)4-34 heavy chain complimentary-determining (HCDR1) and framework region CFR2 sequences. These findings in a Chinese population suggest subtle geographical differences in IgV(H) gene usage while the remarkably specific pattern of SHM suggest that a relatively limited set of antigens may be involved in the development of this disease worldwide. IgV(H) gene mutation status was a significant predictor of initial survival in CLL/SLL. However, an influence of karyotype on prognosis was not observed.