Tobramycin nebuliser solution (TNS) has been investigated in several clinical trials, including a large, placebo-controlled study that demonstrated efficacy over a 24-week period. The open-label extension phase of this trial enabled observations to be conducted for an additional period of almost 18 months. Patients from both treatment arms (n=396) entered the open-label phase and received up to nine 28-day on, 28-day off cycles of TNS 300 mg by aerosol twice daily (b.i.d.). Mean lung function in patients who had received placebo during the double-blind phase improved during the first three cycles of the open-label treatment. However, lung function in these patients did not recover to the levels seen in those patients who had received TNS throughout the double-blind and open-label phases. In both groups of patients, improvement was maintained during the study. Greater improvements were seen in adolescents compared with older patients. Adverse events were generally uncommon, with a notably lower incidence of fever, anorexia, abdominal pain and vomiting than was observed in the double-blind phase among patients who received placebo, and a generally low incidence of tinnitus. We conclude that long-term TNS administration is safe and effective.