The authors define small airways disease and then describe its anatomical characteristics. In the early stage bronchial inflammation is found along with arterial lesions. As the disease develops, there are multiple bronchial and vascular alterations, often accompanied by emphysema. The few existing studies of the morphology/lung function test correlation show a relationship between small airways disease and abnormal respiratory function tests. One of the aims was to find the most sensitive and specific tests using the smoker as a model. However, as only 25% of smokers develop clinical abnormalities, the main problem is probably not early screening, but finding the parameter with the highest prognostic value. This should be the FEVI, measured at about age 40. At a younger age, the information is still too incomplete. More studies are needed to justify early screening. Finally, the authors discuss the procedure to be followed when abnormalities are detected, and its possible consequences on lung function and behaviour.