In cystic fibrosis (CF) patients early antibiotic treatment of lung infection has been shown to lead to Pseudomonas aeruginosa eradication. The present study determined: 1) the time period from eradication to new P. aeruginosa acquisition; 2) P. aeruginosa re-growth and new acquisition; and 3) the impact of eradication therapy on lung function, antimicrobial resistance, emergence of other pathogens and treatment costs. Ciprofloxacin and colistin were used to eradicate P. aeruginosa in 47 CF patients. Bacterial pathogens, lung function decline, P. aeruginosa antimicrobial resistance and anti-pseudomonal serum antibodies were assessed quarterly and compared with an age-matched CF control group. Additionally, costs of antibiotic therapy in both groups were assessed. Early antibiotic therapy leads to a P. aeruginosa free-period of a median (range) of 18 (4-80) months. New acquisition with different P. aeruginosa genotypes occurs in 73% of episodes. It also delays the decline of lung function compared with chronically infected patients, prevents the occurrence of antibiotic resistant P. aeruginosa strains, does not lead to emergence of other pathogens, and significantly reduces treatment costs. The treatment substantially lowers P. aeruginosa prevalence in CF. In conclusion, early antibiotic therapy exerts beneficial effects on the patient's clinical status and is cost-effective compared with conventional antibiotic therapy for chronically infected cystic fibrosis patients.