Malnutrition was once thought to be an inevitable consequence of cystic fibrosis (CF). It is now considered preventable but still contributes considerable morbidity in children. Malnutrition is linked to poorer pulmonary function, reduced survival and quality of life. As the anticipated lifespan of children with CF continues to lengthen, the prevention of malnutrition attains greater importance. This review explores the complex organic and psychosocial factors implicated in the aetiology of malnutrition associated with CF.