OBJECTIVE:This study was performed to investigate frequency and antimicrobial susceptibility of pulmonary pathogens in cystic fibrosis (CF) patients. METHODS: 129 pediatric patients with CF were enrolled in this cross-sectional study. Microbiological cultures were performed based on sputum or pharyngeal swabs. Antibiotic susceptibilities of the isolated bacteria were determined by the disk diffusion method. RESULTS: The main infecting pathogens were Pseudomonas aeruginosa (38.8%), Klebsiella pneumoniae (11.6%) and Staphyloccus areus (9.3%), respectively. The most active antibiotics included rifampin (91.7% susceptibility), vancomycin (85%) and imipenem (83.5%). Emerging resistance against aminoglycosides was observed. CONCLUSION: Regarding in vitro susceptibility results, cyclic treatment of long-term oral azithromycin and inhaled tobramycin could prophylactically be applied, and during exacerbations, imipenem or ceftazidime in combination with an aminoglycoside such as amikacin could be considered the drugs of choice.