Cytogenetic analyses by G-banding and/or Q-banding techniques of leukemic B cells were performed in 102 patients with chronic lymphocytic leukemia (CLL), including six with prolymphocytic leukemia (PLL), one with hairy cell leukemia (HCL), and one with Waldenstrom's macroglobulinemia (WM) from 1979 through 1983. Follow-up after cytogenetic study ranged from 24 to 70 months. Seventeen patients had stage 0, 10 had stage I, 31 had stage II, and 44 had stage III or IV. Adequate metaphases were obtained for karyotypic analysis in 86 (84%) of 102 patients. Of these 86 patients with adequate metaphases, 43 had normal karyotypes (50%) and 43 had abnormal karyotypes (50%), of which trisomy 12 was the most frequent. Ten patients had trisomy 12 as the sole abnormality, 14 had trisomy 12 in combination with other abnormalities, and the remaining 19 had other abnormalities without trisomy 12. Abnormal karyotypes were more frequently associated with patients with advanced stages than those with early stages of the disease. Response rate to chemotherapy was significantly higher in patients with normal karyotypes than in those with abnormal karyotypes. Of eight patients who subsequently developed Richter's syndrome, seven initially had complex karyotypic changes with or without trisomy 12. These observations suggest that the chances of development of Richter's syndrome in CLL patients with multiple chromosome changes may be much higher than in those with either simple trisomy 12 or a normal karyotype. Mean frequency of abnormal metaphases was significantly higher in patients with complex trisomy 12 in combination with other changes than in those with trisomy 12 as the sole abnormality.(ABSTRACT TRUNCATED AT 250 WORDS)