Article type: Original Article Background: Cystic fibrosis (CF) is a genetic disease with an autosomal recessive pattern of inheritance. CF caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and characterized by impaired transport of chloride ions across the cell membrane. Staphylococcus aureus, Pseudomonas aeruginosa, and Burkholderia cepacia have been identified in the cultures of respiratory secretions of CF patients, and infections of these microorganisms are associated with high rates of morbidity and mortality. In patients with CF, severe inflammation of the airway can cause advanced bronchiectasis, which may result in respiratory failure and death. Objectives: This study aimed at evaluating the clinical findings of laboratory tests, bacterial colonization, and drug resistance in children and young adults with CF who hospitalized at the Pediatric Pulmonary Department of Masih Daneshvari Hospital, Tehran, Iran.