Diarrhea among the 11 million children attending day-care centers in the United States is common, but infection control of enteric pathogens in the day-care center setting remains a challenge. In August 1989, an outbreak of cryptosporidiosis was investigated at a day-care center in Georgia. A total of 49% (39/79) of children and 13% (3/23) of staff members who submitted stool specimens were found to be infected with Cryptosporidium. A total of 77% (30/39) of infected children had mild-to-moderate diarrhea (median duration, 5 days). Children were at highest risk if they were less than age 36 months, in diapers, and not toilet trained. Serial stool specimens were collected from 12 infected children. After diarrhea had ceased, oocyst shedding continued in all children for a mean duration of 16.5 days. It is concluded that the prevalence of asymptomatic infections and the duration of shedding after the end of symptoms may previously have been underestimated. Cohorting or exclusion from the day-care center of children who are asymptomatic shedders is not practical, and the management of cryptosporidiosis in day-care centers remains a major challenge.