Cyclospora cayetanensis is an Apicomplexa protozoa which was found to cause gastroenteritis in humans in 1979. This paper reviews the laboratory diagnosis of the disease. The usefulness of direct examination of fresh fecal matter with special acid-fast stains is emphasized as well as the morphometric differentiation between this organism and other similar coccidia. The paper reviews the sporulation technique of Cyclospora cayetanensis for the recognition and differentiation of artifacts and green-blue algae. Another aspect discussed is the morphology of the parasite in histological sections and with electromicroscopic examination whereby tissue morphology changes caused by the microorganism can be identified. The experience of the Service and Laboratory of Parasitology of the Instituto Nacional de Pediatría of Mexico in the laboratory diagnosis of this protozoosis is described. The paper is oriented towards the inclussion of Cyclospora cayetanensis in the diagnostic protocols for the study of diarrheas in our health Institutions.