Poor linear growth and inadequate weight gain are very common problems in cystic fibrosis (CF) children. The most important factors involved in growth failure are undernutrition or malnutrition, chronic inflammation, lung disease, and corticosteroid treatment. Nutritional support and pharmacological therapy with recombinant human growth hormone are essential for a good management of children with CF, although these children are shorter and lighter than healthy children, and despite the catch-up growth observed after diagnosis, deficit in length/height and weight continues to be seen until adulthood. Early diagnosis is essential to ensure better nutritional status and growth, potentially associated with better respiratory function and prognosis. The aims of this review are try to explain etiology and pathogenetic mechanisms of growth failure in CF children and clarify their role in the disease morbidity and in clinical outcome, especially in relation to progressive decline of pulmonary function.