Diarrhea is the pathophysiological reaction of host's gastrointestinal tract to a variety of external stimuli. Classified as a clinical syndrome, diarrhea is the leading cause of mortality and morbidity worldwide. Clinical manifestations can occur in two major forms: A) acute, which usually resolves in less than three weeks and B) chronic, which can last for months. Because of its impact on the host immune system, acquired immune deficiency syndrome (AIDS) is currently the major cause of chronic diarrhea in many parts of the world. It is estimated that up to 90% of HIV-infected individuals with symptoms of AIDS exhibit clinical diarrhea [9, 74, 55]. In SIV-infected rhesus macaques, intense infiltration of intestinal lamina propria with virus-containing lymphocytes and macrophages can be found within days after experimental virus inoculation [25, 57]. In addition to acute enteropathy syndrome, viral infection ultimately leads to other alterations of the gastrointestinal tract including persistent and/or chronic diarrhea, a condition similar to untreated AIDS of human patients. In this short review, the chronic diarrhea is presented from the perspective of the non-human primate or simian model of AIDS (SAIDS), and its most common opportunistic and pathogenic co-infections.