The authors have carried out cytogenic examinations in 19 patients suffering from severe ulcero-haemorrhagic colitis. Nine of these patients are the object of the present communication and namely 3 females and 6 males at the age of 17 to 40 with a duration of the disease from 1 to 3 years. The authors find a great number of chromosomal aberrations in the somatic cells in all the 9 patients. The aberrations affect both the number and the structure of the chromosomes (aneuploidy reaching up to 44% and structure aberrations reaching up to 17.5%).