We describe three patients seen at the Instituto Colombiano de Medicina Tropical in Medellin, in whose case the only parasitic agent incriminated as the cause of prolonged diarrhea was the protozoan Cyclospora sp. One patient was treated with a new antiparasitic drug, nitazoxanide, and the other two with trimethoprim-sulfamethoxazole, all with good results. A revision of some aspects of the illness is presented. It is recommended that in cases of prolonged diarrhea, a complete protocol for the study of parasites in faeces be established and that the microscopists be trained to identify the coccidian pathogens.