Among 1072 rectoscopies we found 100 patients (9,3%) with melanosis coli. All patients suffered from a long-standing constipation together with laxative abuse. Anthrachinonic laxatives which are jointly responsible for the cause of melanosis coli are contained in 70% of all laxatives but also in many cholagogues and weight-reducing preparations. Severe inflammation of the colonic mucosa was seldom found. Colitis simplex, often found histologically and cytologically, could be due to increased turn-over of the mucosa cells. The endoscopic finding of melanosis coli is not regarded as an independent clinical picture but as an expression of chronic constipation unsuccessfully treated with laxatives.