Aneuploidy is a state of abnormal and highly variable DNA and chromoso
me content found in both hereditary disorders and human malignancy. Fo
r two decades flow cytometry has allowed a wide-ranging survey of aneu
ploidy in clinicopathological series. Although up to 75 per cent of al
l tumours analysed display aneuploidy, its value as a clinical marker
of biological aggressiveness is still uncertain. New technologies prom
ise to reveal more precisely the genetic and subchromosomal changes th
at constitute aneuploidy and contribute to the malignant phenotype in
human tumours.