Microscopic (also called lymphocytic) colitis and collagenous colitis are two newly recognised clinicopathologic entities of unknown aetiology presenting with chronic watery diarrhoea. In both conditions, the colon appears normal by barium enema and colonoscopy, however, colonic biopsies reveal infiltration of plasma cells and neutrophils within the lamina propria and increased intraepithelial lymphocytes within the surface epithelium. Lack of a thickened collagen band beneath the surface epithelium histologically differentiates microscopic from collagenous colitis. The exact relationship between the two disorders is as yet unknown. The two entities may be variants of the same spectrum of disease or distinct conditions with and without collagen table thickening. The present case report shows progression of microscopic colitis to collagenous colitis in sequential colonic biopsies taken from a patient during a 7-year endoscopic follow-up suggesting that progression of microscopic to collagenous colitis is a possibility and the two diseases are likely to represent variants of the same condition.