Amongst 141 patients with B-CLL, 53% had an abnormal karyotype. Treatment free survival was shorter in those with karyotypic abnormalities, and especially in those with multiple abnormalities. Multiple abnormalities tended to be associated with progressive disease. Trisomy 12 alone carried no worse a prognosis than a normal karyotype. 49% of patients with stage AO disease had an abnormal karyotype.