Cystic fibrosis is a severe monogenic disorder of ion transport in exocrine glands. The basic defect predisposes to chronic bacterial airway infections with Staphylococcus aureus, Haemophilus influenzae, Pseudomonas aeruginosa and Burkholderia cepacia. The Pseudomonas infections in cystic fibrosis are a paradigm of how versatile environmental bacteria can conquer, adapt and persist in an atypical habitat and successfully evade defence mechanisms and chemotherapy in a susceptible host. Regular chemotherapy with aerosol and systemic antipseudomonal drugs has improved the course and prognosis of the disease, and research for effective vaccines is on the way.