This current study will be coordinated by the CF research team at CHRMC and aims to enroll 520 patients at approximately 50 participating sites across the United States. The contemporary cohort will include patients with CF who are ages 6 years and older and able to expectorate sputum. Patients will be enrolled from many of the same CF centers that participated in the phase 3 trials of inhaled tobramycin, and eligibility criteria will be similar to those used in the phase 3 trials. Subjects enrolled in the contemporary cohort will have a single study visit to obtain a sputum sample that will be sent to a central laboratory for culture and susceptibility testing.