What is the severity of cystic fibrosis?

Variable: This depends on the individual patient. There are several hundred CF mutations that have varying degrees of severity. The most common mutation, df508, can cause failure to thrive in infants, recurrent and very serious lung infections during childhood and often pancreatic insufficiency in children. While early diagnosis and preventive treatment have improved, CF is still a fatal disease.

Depends!: There are many different potential mutations which can cause cystic fibrosis. The traditional ones usually cause severe recurrent lung infections/pneumonias, problems with the pancreas and other complications. There are others that are not nearly as serious. Genetic testing is available for the more serious mutations.