A cytogenetical analysis of chromosomal aberrations, sister chromatid exchanges (SCEs), C-band heteromorphisms and nucleolar organizer regions was done in lymphocytes of 30 patients with precancerous lesions of the uterine cervix progressed to carcinoma and of 30 patients with nonprogressed lesions in a period of 60 months follow-up, in order to identify if any differences existed between low-risk and high-risk dysplasias. Increased frequency of chromosomal breaks, SCEs and C-band heteromorphisms of chromosome 1 and decreased activity of ribosomal genes was observed in patients with dysplasias progressed to carcinoma compared to that of nonprogressed precancerous lesions. The present study thus suggests an intimate relationship between the constitutional chromosomal phenotypes and development of cancer, and these may serve as useful biological markers in defining dysplasias at high risk to progress to cancer.