Although the median survival for patients with cystic fibrosis (CF) is 32.9 years, a small group of patients live much longer. We analyzed the genotype and phenotype of CF patients 40 years and older seen between 1992 and 2004 at the National Jewish Medical and Research Center (n = 55). These patients were divided into two groups according to age at diagnosis: an early diagnosis (ED) group, median age at diagnosis 2.0 years (range 0.1-15 years, n = 28), and a late diagnosis (LD) group, median age of diagnosis 48.8 years (range 24-72.8 years, n = 27). Consistent with the hypothesis that the CFTR genotype affects the age at diagnosis, CFTR DeltaF508 homozygous individuals were more common in the ED group. Although patients in the ED group were predominantly male, the majority of LD patients were female. Patients with CF diagnosed late had a significantly lower prevalence of pancreatic insufficiency and CF-related diabetes, and better lung function. Fewer patients in the LD groups were infected with Pseudomonas aeruginosa, whereas a greater percentage had cultures positive for nontuberculous mycobacteria. This is the largest cohort of older patients with CF described to date, and our findings indicate that patients diagnosed as adults differ distinctly from survivors of long-term CF diagnosed as children.