BACKGROUND: Clinical and therapeutic patterns of ulcerative colitis (UC) are variable in different world regions. The purpose of this study was to examine two close independent southern European UC populations from 2 bordering countries and observe how demographic and clinical characteristics of patients can influence the severity of UC. METHODS: A cross-sectional study was conducted during a 15-month period (September 2005 to December 2006) based on data of 2 Web registries of UC patients. Patients were stratified according to the Montreal Classification and disease severity was defined by the type of treatment taken. RESULTS: A total of 1549 UC patients were included, 1008 (65%) from northern Portugal and 541 (35%) from Galicia (northwest Spain). A female predominance (57%) was observed in Portuguese patients (P