Introduction Chronic ulcerative colitis is usually regarded as a ubiquitous disease without geographic limitations, preferences, or restriction to a particular race, age, or sex. Only very few observations seem to point to a variation in frequency in different parts of the world. It has been stated, for instance, that the disease is less common in the southern than in the northern American continent.1Bockus2reports that ulcerative colitis is more common in the northern than in the southern states of the United States, and this was confirmed by McMahon and Morton.3Lief, in the discussion to the latter report,4states that only relatively few cases of ulcerative colitis occurred among Negro patients, who amounted to more than 50% of admissions in the hospital studied. Melrose5found that the disease was significantly less frequent in the northern than in the southern area of Great Britain. While working in an area