To determine the actual number of deaths from cystic fibrosis reported in 1957 in California, all death certificates mentioning any one of the various terms used to describe the condition were reviewed. As a cause of death, cystic fibrosis is infrequently mentioned on death certificates. In 1957, only 42 of a total of 124,082 death certificates mentioned cystic fibrosis. Half of the deaths occurred in persons less than 12 months of age. There was no significant difference by sex between deaths due to cystic fibrosis and deaths from all causes. All deaths occurred in the white population.