In June 1985, we investigated an outbreak of cryptosporidiosis at a day-care center in Florida. Through day-care center-wide stool screening, 33% (28/84) of the children and 22% (4/18) of the staff members submitting stool specimens were found to have cryptosporidiosis. Children 12–35 months of age and their teachers were at highest risk. All but 1 of the Cryptosporidium-positive patients reported diarrhea, which lasted between 1–44 days. Serial stool specimens were obtained from 8 infected individuals (5 children and 3 adults). Duration of oocyst shedding ranged from 8 to more than 50 days and continued in 5 individuals after diarrhea ceased. No relationship was found between duration of oocyst shedding and the age of the patient or duration or severity of diarrhea. Results of the investigation indicate that infected individuals may continue to excrete oocysts and, therefore, may remain infectious for days or weeks after gastrointestinal symptoms disappear.