In conclusion, the causes of chronic diarrhea in the returned traveler are protean. Careful evaluation requires an understanding of where the traveler has been, when they were there, the type of diarrheal illness, medications taken, and knowledge of the patients' other medical problems. Protozoa, particularly G. lamblia, C. parvum, and C. cayatenensis, are among the more commonly identified agents. If the patient is immunocompromised, microsporidia and Isospora become more likely, and a prior history of antimicrobial use raises the possibility of C. difficile colitis. Occasionally helminths, which establish intimate contact with the intestinal mucosa, may also cause prolonged diarrhea. If these and other gastrointestinal insults, such as tropical sprue, small bowel overgrowth, lactose intolerance, and processes unrelated to travel are excluded by more invasive studies or clinical history, the patient can be reassured that idiopathic chronic diarrhea is usually self-limited.