Among the proposed classifications for pediatric ILD, one strategy frequently used is to separate the primary pulmonary disorders and the systemic disorders with pulmonary involvement. Recently, an additional group has been introduced which is based on the concept that some pediatric ILD are observed more frequently in infants, while others are more specific to older children. The last ERS monography on ILD provided a chapter on pediatric classification which is based on a clear distinction between children aged 0-2 years and children over 2 years-old [7] . Indeed the stage of lung development and maturation should be taken into consideration when approaching a diagnosis of pediatric ILD. In this view, a new term "diffuse lung disease" has recently been introduced that comprises a diverse spectrum of lung disorders with impaired gas exchange and diffuse infiltrates by imaging. These disorders, more prevalent in young children, include diffuse developmental disorders, lung growth abnormalities, neuroendocrine cell hyperplasia and pulmonary interstitial glycogenosis, surfactant dysfunction disorders, disorders related to systemic diseases, disorders of immunocompromised host, and disorders of normal host caused by various insults such as aspiration syndrome or infections [8] . Some diseases are mostly observed in older children such as systemic diseases, idiopathic disorders as described in adults (DIP, UIP, NSIP and lymphoid interstitial pneumonia (LIP)), unclassifiable ILD and also infectious disorders [9] .