The clinician presented with a child who has chronic diffuse infiltrates must entertain a vast array of potential diagnoses. A systematic, step-wise approach using the medical history and physical examination and a combination of noninvasive and invasive studies will provide a specific diagnosis in most, but not all, children with interstitial lung disease (ILD). Comprehensive supportive care should be given to all patients and specific therapy applied when available. Anti-inflammatory therapy, usually with corticosteroids, is indicated for most forms of idiopathic ILD. The prognosis of children who have ILD is variable. A simple Severity of Illness Score may predict survival in these patients.