The persistent isolation of Pseudomonas aeruginosa in the airways of non-cystic fibrosis bronchiectasis (NCFB) patients is associated with a worsening of the symptoms, increase of exacerbations, poor quality of life and functional impairment. The objective of this study was the analysis of the eradication rate of P. aeruginosa in the sputum of patients with NCFB treated with inhaled colistin and the effects of the treatment in the exacerbations. This was a prospective, cohort, study of 67 NCFB patients treated with inhaled colistin at the Hospital of A Coruña (Spain). We recorded dyspnoea, exacerbations, lung function and sputum cultures of P. aeruginosa in the patients. The mean age of the patients was 67.25 ± 14.6 years (59.7% male). The percentages of eradication of P. aeruginosa in sputum at 3, 6, 9 and 12 months were 61.2%, 50.7%, 43.3% and 40.3%, respectively. We observed a significant decrease in exacerbations after 1 year of colistin treatment (1.98 ± 3.62) versus the previous year (3.40 ± 4.21, p < 0.001). We conclude that treatment with inhaled colistin in patients with NCFB and P. aeruginosa in sputum can achieve high rates of eradication even in patients with several previous positive cultures, as well as a significant decrease of exacerbations and hospital admissions.