Microscopic colitis (MC), collagenous colitis (CC) and lymphocytic colitis (LC), represent a pathological entity causing chronic secretory diarrhea with endoscopically normal colon. Histological diagnosis is obtained by biopsies done throughout the colon. CC is defined by the thickening of the subepithelial collagen band of more than 10 pm and LC by more than 20% intraepithelial lymphocytes per epithelial cell. The incidence of MC has been steadily increasing and the prevalence of MC varies from 10-14% in patients with chronic diarrhea and endoscopically normal colon. The clinical presentation of MC is very close to that of functional diarrhea. The recent introduction of a new drug and autoimmune disease are the main factors associated with MC, and there is a special association with celiac disease is. Although rare complications can occur, MC are benign pathologies. Therapeutically, it is first necessary to eliminate a drug-induced, drug discontinuation allowing the cure of colitis, and an associated celiac disease. In other cases, budesonide is the treatment of choice for the moderate to severe forms resistant to the usual symptomatic treatments; relapse is however frequent after the withdrawal of budesonide, and may necessitate its continuation at the lower possible dose.