It is estimated that about 60–70% of Cystic Fibrosis patients develop Pseudomonas aeruginosa chronic infection,with progressive loss of lung function, as well as increased antibiotic resistance and mortality. The current strategy is to maintain lung function by chronic suppressive antipseudomonas antibiotic therapy. Tobramycin inhalation solution was the first approved aerosolised antibiotic to be used against P. aeruginosa; inhalatory tobramycin frequency of administration is twice daily and inhalation time is estimated to be 15 to 20 min. From the pharmacokinetic point of view, aminoglycosides are dose-dependent antibiotics and therefore once-daily dosing intravenous regimens have shown to be superior to the conventional multiple daily dosing. Therefore, there is no pharmacological reason to prefer the b.i.d administration as it is usually performed in current clinical practice. Should this be confirmed also for inhalatory route, the use of once-daily dosed aerosolized tobramycin could be an important step in making treatment burden easier in CF patients. The aim of this proof of concept study was to explore the effectiveness of treatment with once daily inhaled tobramycin in reducing P. aeruginos a density in sputum of chronically infected patients.