Pseudomonas aeruginosa is one of the primary pathogens in the cystic fibrosis (CF) lung and a significant cause of morbidity and mortality. Reports of the spread of epidemic or transmissible strains of P. aeruginosa within and across CF centres in Europe have raised concern regarding the possibility of clonal spread among and within CF centres in Ireland. P. aeruginosa isolates (313 isolates from 142 sputum samples and 53 throat swabs) from 68 CF patients were examined using PFGE to explore the diversity of P. aeruginosa isolates among CF patients in a Dublin paediatric hospital. Only 57 different P. aeruginosa genotypes were identified among the 313 isolates. Forty-three of the genotypes were observed only in individual patients (distinct genotypes) while 13 cluster strains (present in two to four patients) were observed. Typing of P. aeruginosa isolates identified one indistinguishable clonal isolate of P. aeruginosa present in 13 CF patients (13/68; 19.1 %) which displayed higher levels of antibiotic resistance than those displayed by P. aeruginosa isolates of distinct genotype.