A newly recognized protozoan human parasite, Cyclospora has been incriminated as the cause of prolonged diarrhea. Five patients had episodes of diarrhea accompanied by nausea, weight loss, and/or low-grade fever for 10–45 days. Multiple fecal samples fixed in sodium acetate-acetic acid-formalin contained spherical organisms measuring 8–10 µm in diameter; a modified concentration technique was used to detect them. The sediment was examined by direct microscopy and autofluorescence, and the identification was confirmed by acid-fast stain. All patients had visited either Mexico or Thailand. The presence of Cyclospora organisms in these patients shows that these can be etiologic agents of traveler's diarrhea in both immunocompetent and immunocompromised hosts. Fecal specimens from patients with unexplained diarrhea should be routinely examined for their presence.