A cytogenetic study was performed in five patients with Sezary syndrom
e. Metaphases were obtained from a phytohemaggluyinin-stimulated lymph
ocyte culture. The five patients showed abnormal karyotypes. The chrom
osomes preferentially involved in numerical aberrations were chromosom
es 10 (monosomy) and 13 (monosomy); involved in structural changes wer
e chromosomes 1, 2, 4, 6, and 14. In our series, all patients showed p
rogression of the disease.