Pulmonary insufficiency is the main cause of death in cystic fibrosis (CF). We analysed forced expiratory volume in 1 s (FEV1) data of 14,732 patients registered in the European Cystic Fibrosis Society Patient Registry (ECFSPR) database in 2007. We used linear and logistic regressions to investigate associations between FEV1 % predicted and clinical outcomes. Body mass index (BMI), chronic infection by Pseudomonas aeruginosa, pancreatic status and CF-related diabetes (CFRD) showed a statistically significant (all p<0.0001) and clinically relevant effect on FEV1 % pred after adjusting for age. Patients with a lower BMI experience a six-fold increased odds ratio (95% CI 5.0-7.3) of having severe lung disease (FEV1 <40% pred) compared to patients with normal BMI. Being chronically infected with P. aeruginosa increases the odds ratio of severe lung disease by 2.4 (95% CI 2.0-2.7), and patients with pancreatic insufficiency experience a 2.0-fold increased odds ratio (95% CI 1.6-2.5) of severe lung disease compared to pancreatic sufficient patients. Patients with CFRD have a 1.8-fold increased odds ratio (95% CI 1.6-2.2) compared to patients not affected. These potential risk factors for pulmonary disease in patients with CF are to some degree preventable or treatable. We emphasise the importance of their early identification through frequent routine tests, the implementation of infection control measures, and a timely initiation of relevant therapies.