Detection of Cryptosporidium parvum is not routinely done in laboratories of clinical microbiology and there is no obligation to communicate isolations of this pathogen to health authorities. For these reasons, frequency of cryptosporidiosis and sources of infection are only poorly known in Switzerland. To obtain more concise information in this field, feces from 5179 hospitalized and 1256 ambulatory patients with suspected gastrointestinal infections were screened for Cryptosporidium spp. over the period of one year in two laboratories. In toto, 13 patients with cryptosporidiosis were detected which results a frequency of 0.2%. Furthermore, it was shown by a projection that about 340 cases of cryptosporidiosis have to expected yearly in Switzerland, resulting an estimated morbidity of 4.85 cases per 100,000 persons. With regard to risk factors, the available patient data did not allow solid statistical conclusions. However, known risk factors such as immunosuppression, travelling abroad (33.3%) and contact to symptomatic persons were unquestionably demonstrated. Oysters, raw milk and cream from raw milk had to be strongly taken into consideration as food vehicles of transmission. Tap water from municipal nets has not to be considered as relevant source of sporadic infections. The obtained data indicate that cryptosporidiosis is a disease of low epidemiological significance in Switzerland. To a great extent, cryptosporidiosis could be prevented by best known measures of personal hygiene, avoiding certain raw food-stuffs and being aware of safe catering on travels.