α-1 antitrypsin is synthesised in the liver and protects lung alveolar tissues from destruction by neutrophil elastase. α-1 antitrypsin deficiency is a common autosomal recessive condition (1:1600 to 1:1800) in which liver disease results from retention of abnormal polymerised α-1 antitrypsin in the endoplasmic reticulum of hepatocytes, and emphysema results from alveolar wall damage. The clinical consequences of α-1 antitrypsin deficiency in childhood are haemorrhagic disease in infancy, cholestasis in infancy, or chronic liver disease. Lung disease attributable to α-1 antitrypsin deficiency does not occur in childhood, but is closely linked to smoking in adults. Membranoproliferative glomerulonephritis, panniculitis, and necrotising vasculitis are associations with α-1 antitrypsin deficiency in adult life.