In most cases the ano-cutaneous clinical symptoms correlated to diseases of the gastro-intestinal tract are not specific (erythema, itching, wounds or scarring). However in the following diseases occasional dermatological lesions may directly contribute to their diagnosis: in Crohn's disease, tuberculosis of bowel, chronic entamoebiasis and bilharziosis, the skin lesions of the anal area have the same histological structure as the gut lesions. Perianal fistulas and ulcers are frequent in Crohn's disease especially if there is a colonic and rectal spreading; they respond badly to steroid therapy and are often correlated with a worse prognosis. Perianal specific lesions occur often in oxyuriasis in children, in candidiasis of the digestive tract, in systemic aphthosis and in some malignancies. In other gastro-intestinal disturbances, the dermatological and features are less specific and can only be suggestive: iatrogenic and microbial diarrheas, side-effects of laxatives, proctological diseases. It has to be emphasized that pruritus ani is only induced by deeper lesions when they spread to the perianal skin. In proctological practice, contact dermatitis by sensitivity to anaesthetics or suppository balsams (Peruvian balsam), itching or burning atrophy by topical steroid abuse, non-diagnosed fungal (candidiasis), bacterial (erythrasma) or psoriatic intertrigos (flexural psoriasis) may sometimes explain the failure of therapy.