Data from 17,857 patients with cystic fibrosis submitted in 1990 to the registry maintained by the Cystic Fibrosis Foundation were used to described their demographic characteristics, survival rates, pulmonary function, anthropometry, microbiologic data, complication rates, and health care utilization. Comparisons with similar data collected in 1969, 1972, and 1978 demonstrated a significant shift in the age distribution of patients with cystic fibrosis. The proportion of adult patients increased fourfold between 1969 (8%) and 1990 (33%). In 1990 the median age of all patients in the cystic fibrosis registry was 12.5 years; the median age at diagnosis was 7 months; cystic fibrosis was diagnosed in 90% of all patients by age 12 years. Meconium ileus at birth was reported for 16% of all patients with a new diagnosis in 1990. Median survival age doubled between 1969 and 1990, from 14 to 28 years. Female patients consistently had a lower median survival age than male patients (25 vs 30 years in 1990). The most frequently reported respiratory pathogen was Pseudomonas aeruginosa, cultured in specimens from 61% of all patients, ranging from 21% of those less than 1 year of age to more than 80% of those aged 26 years or older. Overall, patients with cystic fibrosis are living much longer than in the past but still have chronic pulmonary infections and other medical complications related to their disease, including diabetes, intestinal obstruction, cirrhosis, hemoptysis, and pneumothorax.