Diffuse interstitial lung disease (DILD) represents a heterogeneous group of disorders characterised by restrictive lung function and impaired gas exchange. As these diseases occur on a background of the developing lungs and immune system, the clinical presentation and disease progression is modified by comparison with their adult equivalents; thus, often differs markedly in presentation, clinical features and progress from ILD in adults, and it is not safe to extrapolate from adults to children. It is important to understand the normal growth and development of the lungs in children to understand the development of interstitial lung disease. As the chest radiograph is often non-specific, HRCT has been shown in adults and children to increase the accuracy at diagnosis of diffuse lung disease. The trade-off in sensitivity and specificity of HRCT over chest X-ray is related to radiation dose which is significantly higher with conventional spiral or volumetric CT; however, the use of low-dose (50 mA, 0.75 s) limited (1-mm slices every 15-20 mm) HRCT in inspiration with three expiratory supplementary scans allows accurate assessment of the presence and extent of diffuse lung disease at a dose equivalent to approximately ten chest radiographs. Images are reconstructed on a high spatial resolution algorithm and displayed with a wide window setting, at a width of 1500 Hounsfield units (HU) and at a level of -500 HU.