AbstractSequential cytogenetic studies were performed on a minimum of two and a maximum of nine occasions (mean 3.6) on the peripheral blood leucocytes of 112 patients with B‐CLL. On initial cytogenetic analysis, 58 had a normal karyotype and 64 had a clonal abnormality. Karyotypic evolution occurred in 18 patients (16%). There was no significant difference in the incidence of disease progression between patients with a stable karyotype and those who underwent karyotypic evolution. In only one patient was there a clear association between disease progression, a change in cell morphology and karyotypic evolutio