Pseudomonas aeruginosa is isolated in sputum cultures from cystic fibrosis (CF) patients and adults with bronchiectasis (BS) and chronic obstructive pulmonary disease, but it is not well known if the characteristics of colonization in these latter patients are similar to those with CF. We examined 125 P. aeruginosa isolates obtained from 31 patients suffering from these diseases by pulsed field gel electrophoresis and genotyping of mucA and fpvA genes. The pattern of colonization, with dominance of a clonal strain and incidence of mucoid phenotypes, was similar in every group of patients; however, in some CF and BS patients, we detected the replacement or coexistence of 2 main clones. The main differences were found in the nucleotide position of less common mucA mutations, other than mucA22, and in the predominance of the different types of the pyoverdine receptor. Our results support a similar colonization pattern by P. aeruginosa in the different obstructive pulmonary diseases.