Diffuse panbronchiolitis (DPB) is an idiopathic inflammatory disease, well recognised in Japan and principally affecting the respiratory bronchioles, causing a progressive suppurative and severe obstructive respiratory disorder. If left untreated, DPB progresses to bronchiectasis, respiratory failure and death. It was first described in the early 1960s. Subsequently, in 1969, the disease was named DPB to distinguish it from chronic bronchitis. "Diffuse" refers to the distribution of the lesions throughout both lungs, and "pan-" refers to the involvement of inflammation in all layers of the respiratory bronchioles. The distinctive imaging and histological features, the coexisting sinusitis, and the isolation of Haemophilus influenzae and Pseudomonas aeruginosa in the sputum enhance disease recognition. Histologically, DPB is characterised by chronic inflammation, localised mainly in the respiratory bronchioles and adjacent centrilobular regions, with characteristic interstitial accumulation of foamy histiocytes, neutrophils and lymphocyte infiltration. Neutrophils and T-lymphocytes, particularly CD8+ cells, together with the cytokines interleukin-8 and macrophage inflammatory protein-1, are believed to play key roles in the development of DPB. A significant improvement in the prognosis of this potentially fatal disease has been recently reported thanks to the use of long-term therapy with macrolide antibiotics, the effect of which is attributed to an anti-inflammatory and immunoregulatory action.