Background and objective: Clonal strains of Pseudomonas aeruginosa have been identified in large cystic fibrosis (CF) centres. Whether such strains are more virulent or whether cross-infection between patients explains their widespread prevalence is unknown. This study described the epidemiology of P. aeruginosa infection in CF patients in Tasmania, Australia, an area with a high CF birth incidence. Patients in Tasmania are geographically dispersed and when this study was conducted (2003) there was no central CF clinic, with patients receiving treatment in regional hospitals. Methods: P. aeruginosa isolates from CF adults aged 15 years and over in Tasmania were genotyped using random amplified polymorphic DNA (RAPD)-PCR and clonal strains confirmed with pulsed field gel electrophoresis. Results: Airway samples were obtained from 41 patients (82% of the adult CF population). P. aeruginosa was isolated from 34 patients and nine (26%) of these individuals harboured P. aeruginosa strains with identical RAPD-PCR and pulsed field gel electrophoresis patterns (Australian Epidemic Strain III – AES III). AES III was isolated from patients in all regions of Tasmania and was distinct from the epidemic CF strains described on mainland Australia (AES I and II). The possible link between CF adults infected with AES III was attendance at family camps more than 12 years previously. Patients harbouring AES III had suffered significantly more exacerbations requiring hospitalisation during the 2 years prior to the study compared with patients infected with unique strains (P