[Collagenous colitis; an invisible disease?].

A middle-aged female with chronic diarrhoea was diagnosed after extensive evaluation as having collagenous colitis. Remarkable in this case was the definitely abnormal-looking mucosa in a period of clinical exacerbation whereas the subepithelial collagenous band completely disappeared in a clinically more quiet stage of the disease. The diagnostic importance of performing stepwise colonic biopsies even in normal-appearing colon in a patient with chronic undiagnosed diarrhoea is discussed.