Lung disease and Pseudomonas aeruginosa (P. aeruginosa) airway colonization represent a major cause of morbidity and mortality in cystic fibrosis (CF). Human beta-defensin (hBD)-1 is believed to play an important role in mucosal innate immunity in the lung. This study aimed to investigate whether three single-nucleotide polymorphisms (SNPs) in the 5'-untranslated region of DEFB1, G-52A, C-44G and G-20A were associated with P. aeruginosa airway colonization in CF. A total of 224 CF patients and 196 control subjects were studied. DEFB1 SNPs were characterized by restriction fragment length polymorphisms. Patients' sputum samples were collected and analyzed by standard methods. Single SNP analysis suggested that CF patients carrying the -52AA and the -20GG genotypes had a higher rate of P. aeruginosa airway colonization than patients homozygous and heterozygous for the -52G and -20A alleles (P=0.01 and P=0.007, respectively). A significant association between the ACG haplotype and chronic P. aeruginosa infection was also identified (odds ratio (95% confidence interval): 3.00 (1.42-6.36), P=0.004). These results indicate that variant alleles in DEFB1 might contribute to the colonization of P. aeruginosa in CF.