Two complete colonoscopic examinations, up to the ileocecal valve, were performed in 51 patients with idiopathic ulcerative proctocolitis. The extent of the disease was assessed as prevalent in the endoscopic and histological observations on biopsy tissue. The mean interval between the two endoscopies was 36 months (minimum interval 3 months). In 58.8% of cases, a variation of extent was observed: in 33.3% with an upward diffusion, in 25.5% with a reduction. In a larger group (51 vs 31) of patients observed for a longer period of time (36 vs 17 months), the findings of Niv et al. were confirmed. No correlation between epidemiological and clinical data and changes in the anatomical extent of colitis was shown. Disease extent does not, therefore, appear to contribute to the prognosis, in particular to the more severe attacks and cancer.