Résumé : BACKGROUND:: Cryptosporidium outbreaks in day-care centers (DCCs) occur commonly. However, controlling spread of infection in these settings is difficult, and data about effectiveness of different control strategies are sparse. In this study, a Cryptosporidium outbreak in a large DCC located in Brussels is described with evaluation of hygienic and therapeutic interventions. METHODS:: During a 3-week period, 43 of 130 children attending the DCC developed enteric symptoms. Stools from 122 children were examined for microbial pathogens. Of them, 38 (31%) were diagnosed with Cryptosporidium, 29 of them being symptomatic (76%) and 9 (24%) asymptomatic. Diagnosis was performed by microscopy, antigen tests, and real-time polymerase chain reaction. Strict infection control measures were implemented during the first week after the start of outbreak. After 4 weeks, 27/38 children (71%) were still symptomatic and Cryptosporidium positive. Because of persisting symptoms and fear of further spread of infection, all 27 children were treated with paromomycin. Two weeks later, 18 of 27 children were asymptomatic and were parasitologically negative. The remaining 9 children, still symptomatic and Cryptosporidium positive, were treated with nitazoxanide. Three weeks later, week 9 after the start of outbreak, all 38 children involved in the outbreak were asymptomatic and Cryptosporidium negative. CONCLUSIONS:: Our study underscores the need to rule out Cryptosporidium etiology in a diarrheal outbreak in a DCC. Rapid implementation of infection control measures can most likely halt the spread of infection. The role of nitazoxanide to limit duration of shedding of oocysts deserves more attention for its use in outbreaks.