This US study was conducted to determine whether mode of diagnosis and initial disease presentation influence lung disease and survival in patients with cystic fibrosis. The study population included 27,703 patients reported to the 1986-2000 Cystic Fibrosis Foundation Registry. Patients were segregated into four diagnostic categories: meconium ileus (MI), prenatal/neonatal screening (SCREEN), positive family history (FH), and symptoms other than meconium ileus (SYMPTOM). When compared with patients in the SCREEN group, those in the MI or SYMPTOM group were found to have significantly greater risks of shortened survival, Pseudomonas aeruginosa acquisition, and forced expiratory volume in 1 second (FEV(1)) below 70% of predicted. In the SYMPTOM group, the greatest risks of shortened survival, P. aeruginosa acquisition, and FEV(1) <70% occurred for patients presenting with combined respiratory and gastrointestinal symptoms, followed by respiratory or gastrointestinal symptoms alone; the best outcomes were in patients with other presenting features. Additionally, patients with presumably "severe" genotypes (DeltaF508 plus other class I, II, III mutations in both alleles) had greater risks of shortened survival and P. aeruginosa acquisition compared with patients with presumably "mild" genotypes (class IV or V mutations in one or both alleles).