Cystic fibrosis of the pancreas was recognized as a separate disease entity 21 years ago, but it is only in the last 10 years that most of the patients have been diagnosed. Pulmonary involvement dominates the clinical picture and determines the fate of the patient. The advent of effective antibiotic agents has been responsible for greatly increasing the life span of many affected individuals, who now frequently reach young adult age. Cystic fibrosis of the pancreas, despite its name, is a generalized disease genetically determined and probably transmitted as a recessive trait. Homozygotes have the fully expressed syndrome with all or most of the clinical manifestations including elevated sweat electrolytes. Their ultimate prognosis is guarded and it is not probable that many of these patients will have a normal life span. Of heterozygotes, children and adults, 20-30% present as the only expression of the disorder an abnormally elevated concentration of Na and Cl in their sweat. In addition a significent number of relatives of index cases have frequent attacks of bronchitis and are subject to so-called "asthma," while a smaller number suffer from more severe chronic respiratory involvement. Much further study is needed to clarify the problems outlined and to interpret the facts brought to light by recent investigations. It is evident, however, that cystic fibrosis in the homozygous and heterozygous state and its possible relation to other types of chronic pulmonary disease presents a problem of increasing importance to the internists and to the specialists in chest disorders. Cystic fibrosis is breaking out of the pediatric bounds to which it had earlier been limited by its high mortality rate in infancy and childhood. It is now invading the domain of disease of the adult individual.