Acute diarrhea is a major problem with high morbidity and mortality rates in developing countries, especially in children. Complex laboratory investigations are required to define the etiology because of the broad spectrum of etiological agents and the non-specific clinical signs. In the last decade, Cyclospora cayetanensis--a new acid-fast coccidian species--was pointed to be the cause of watery self-limited or prolonged diarrhea in immunocompetent and immunocompromised patients, with very good evolution after treatment with co-trimoxazole. Unlike Cryptosporidium parvum, nonsporulated Cyclospora oocysts are eliminated in feces, with no risk of human to human transmission. Cyclospora cayetanensis is widely spread, producing endemic infections, in Asia and South America and was reported to produce infections in foreign travellers in these areas and epidemic outbreaks of foodborne diarrhea. We describe the first case of acute diarrhea associated with Cyclospora cayetanensis in an immunocompetent child admitted to Iaşi "Sf. Maria" Hospital.