In 7 patients seen over 3 years, cystic fibrosis had been wrongly diagnosed. The initial sweat test was misleadingly high in only 3 cases. In 1 case no sweat test had been done, and in 4 one or more normal sweat-test results were ignored. As a result of misdiagnosis 4 children were sent to schools for the physically handicapped and 1 man lost his job in the police. Despite warnings about the limitations of sweat tests and dangers of diagnosing cystic fibrosis without typical clinical features, cystic fibrosis is wrongly diagnosed in substantial numbers of children in England.