It has recently been suggested that there is an association between infectious gastroenteritis and irritable bowel syndrome with chronic diarrhea; and a striking similarity between the microscopic lesion observed in this condition and the lesion described in microscopic colitis (MC). As in developed countries MC is found in only 12.6 to 15% of patients with chronic diarrhea, we thought it worthwhile to investigate in Perú, a developing country with high prevalence of infectious gastroenteritis, the prevalence of MC also in patients with chronic diarrhea.One hundred and ten patients with chronic diarrhea underwent biopsies from the right and left colon, and the biopsies were examined histologically to detect MC of lymphocytic or collagenous type.MC was present in 44 (40%) of the 110 patients with chronic diarrhea, being of lymphocytic type in 42, and of collagenous type in.The prevalence of MC observed in Peruvian patients with chronic diarrhea is high when compared to reports from developed countries. This finding supports the idea that infectious gastroenteritis may, under certain conditions, precipitate the appearance of MC, probably by an autoimmune reaction.