PCR fingerprinting was used for the epidemiological investigation of 64 Pseudomonas aeruginosa isolates collected from 16 chronic bronchiectasis patients without cystic fibrosis: 56% of the patients harbored one clone, 12.5% carried a single major type with minor variants, and 31.5% carried two clones. Only a minority of the acquisitions of antibiotic resistance was related to the acquisition of exogenous strains. Mucoid and nonmucoid sets of isolates did not display any consistent differences in their patterns. The genetic similarity among the clones ranged from 10 to 69%. Cross-infection or common-source exposure did not appear to have occurred.