Objective To probe into the causes and clinical characteristics of diarrhea in patients from different age groups.Method Clinical data of diarrhea patients received in the out-patient of Peking University Hospital from April 2010to March 2012were analyzed retrospectively.Results Among the 252cases of patients

there were 214cases with infectious diarrhea

accounted for 84.9%;38cases with non-infectious diarrhea

accounted for 15.1%.Among patients with non-infectious diarrhea

there were 8cases with malignant bowel tumor

accounted for 3.2%;there were 7cases with irritable bowel syndrome and 7cases with autoimmune bowel disease with a respective percentage of 2.8%;there were 5cases with drug enteritis and 5cases with bowel disease of unknown cause with a respective percentage of 2.0%;others accounted for 2.2%.Major cause of diseases in patients from different age groups was infection.Autoimmune bowel disease and irritable bowel syndrome typically occurred in persons from groups aged less than 30years and groups aged between 30 and 60years

and tumor typically occurred in persons from groups aged above 60years.Among the 247cases of patients with clear etiological diagnosis

there were 215cases with their course of disease shorter than 3 weeks

including 211cases with infectious diarrhea and 4cases with non-infectious diarrhea;among 32cases of patients with a 3-week course of disease or longer

there were 3cases with infectious diarrhea and 29cases with non-infectious diarrhea.Conclusion Diarrhea is mainly caused by infectious diseases and malignant bowel tumor is the major cause of non-infectious diarrhea.