Cystic fibrosis (CF) is a multisystem genetic disorder affecting around 1 in 2,500 live births in the UK. Although all newborns undergo screening for CF, around 15% of infants will present shortly after birth with meconium ileus and some will already have faltering growth when the screening results are available at 3-4 weeks of age. Infants who present with meconium ileus should be treated with a high index of suspicion for CF until proven otherwise. Mucociliary dysfunction leads to accumulation of mucus in the airways and secondary infection. Respiratory symptoms may be non-specific initially and include cough and wheeziness, frequent respiratory infections and, in older children, sinusitis.