The case of a child with apparent cystic fibrosis whose many signs, symptoms, and laboratory results were convincingly portrayed by his mother is presented. The mother falsified the history, and cunningly altered sweat tests and stool fat analyses, and stole sputum from patients with cystic fibrosis to make her child appear to have cystic fibrosis. This case of Munchausen syndrome by proxy highlights the extent to which the diagnosis of cystic fibrosis rests on reliable history and laboratory data and emphasizes the extremes to which perpetrators of this form of child abuse may go to make their case. Medical personnel must educate civil authorities about this syndrome and the dangers it represents to the child.