An outbreak of cryptosporidiosis occurred in East Baton Rouge and Ascension parishes, Louisiana, that was associated with a water spray park. Cryptosporidium isolates from the 35 patients were not subject to genotyping or species determination. A case-control study showed that recreational water use at one commercial water park was the only exposure significantly associated with cryptosporidiosis. No water park samples were collected for testing because the water park had already closed for the season.