A girl and a boy, who both presented with recurrent respiratory infections from birth, were referred to a paediatrician at the age of 2.5 years: they were diagnosed with cystic fibrosis (CF). The girl died from respiratory insufficiency at the age of 6 years and the boy at the age of 13 years from pulmonary aspiration. A further girl and boy who presented with abnormal faeces and failure to thrive were referred to the paediatrician at the ages of 2.5 months with haematomas and 2 weeks with anaemia respectively, as a result of vitamin deficiencies due to malabsorption. They too had CF. The girl had a brain haemorrhage in the meantime that left her with serious impairments. The boy recovered. A delay in diagnosing CF is not uncommon, as the symptoms of CF are hard to differentiate from those of common childhood diseases. However, this diagnostic delay can result in serious organ damage. Current treatment of CF has a predominantly prophylactic character and aims at maintaining normal growth and nutritional status as well as at preventing or postponing chronic bacterial infection of the lower respiratory tract. This treatment is most effective when it is started before any organ damage has occurred: a state that can only be achieved when patients with CF are identified shortly after birth. Therefore, it is important to add CF-screening to the neonatal screening program.