The present work endeavoured to study the possible changes in bowel movement habits of hospitalized patients in medical units at three general hospitals of the County of São Paulo. The purpose was also to verify the types of changes which occured and the causes attributed by the patients relating to bowel movement habits. The population of the study consisted of 200 ambulatory patients, adults of both sexes. The data collecting was carried out by means of applying a questionaire through a structured interview. The results obtained revealed the following conclusions: the majority of the interviewed patients reported changes of the bowel movement habits after being admitted to the hospital. The causes presented by the patients as resoonsible for the changes of the bowel movement were classified in physiological, psychosocial, therapeutical and environmental. The physiological and psychosocial were the most distinguished. The food was the main reason mentioned while the reasons of anxiety, nervousness, worriment were mentioned as phychosocial causes. Only the independently variable sex, influenced in the changes of the bowel movement habits, after a specific statistical investigation