To discover laboratory ascertainment and reporting practice for cases of cryptosporidiosis in two health authority regions, we surveyed laboratories serving Wales and the North West of England for faecal screening policies and methods for detection of Cryptosporidium. Forty-eight of the 49 laboratories responded, of which 39 (81%) screen all stool specimens from symptomatic individuals for Cryptosporidium and 9 (19%) screen selected specimens. Although laboratory screening is more complete than has been reported in other regions, we identified discrepancies where patient age was used as a selection criterion, and we make suggestions to amend this. Forty-two (88%) responding laboratories report confirmed cases to the regional Communicable Disease Surveillance Centre (CDSC) and 45 (94%) report to the local authority environmental health department. We also surveyed local authorities in both regions for policy and practice concerning the investigation of reported cases of cryptosporidiosis in the same regions. All 59 local authorities responded, of which 57 (97%) investigate cases by completion of an exposure questionnaire as well as providing advice on the prevention of spread of infection. Variation in case ascertainment may influence perception of incidence, clusters and outbreaks of cases of cryptosporidiosis.