The medical records of 142 patients with cystic fibrosis were reviewed. The patient group included 78 males and 64 females; three patients were black. Periods of observation ranged from two to 25 years (mean, 14.5 years). The analysis focused on clinical evaluation at age 18 years and included information gained at an earlier age. Evaluation at age 18 years was based on Shwachman and Kulczycki's (S-K) scoring system, Brasfield chest roentgenographic scoring system, pulmonary function measurements, height-adjusted weight percentile, sputum bacteriologic results, number of hospitalizations for treatment of pulmonary infections prior to the age of 18 years, time of onset of clubbing, and frequency of complications. There were no significant differences between the sexes in clinical features. Median survival from the time of diagnosis to the conclusion of the study period (1955 to 1984) was 22 years for females and 25 years for males (NS). Median length of survival beyond the age of 18 years was eight years for females and 12 years for males (NS). Stepwise logistic regression and Cox regression analysis applied to 11 variables identified the S-K clinical score at 18 years of age as the best predictor of survival to the age of 23 years. The median durations of survival after the age of 18 years for patients with clinical scores of 30 to 49, 50 to 64, and 65 to 75 at age 18 were five, seven and a half, and 12 years, respectively (p less than 0.0001). Low clinical score, low weight percentile, and Pseudomonas cepacia colonization of the lower respiratory tract at the age of 18 years indicated a poor prognosis. On the other hand, high clinical score, good weight percentile, and colonization with Staphylococcus aureus alone were likely to be found in patients with mild disease and an increased likelihood of long-term survival with preserved pancreatic function.