The term chronic nonspecific lung disease (CNSLD) was proposed by the Ciba Symposium in 1959 as an umbrella term grouping chronic bronchitis, asthma, emphysema and irreversible or persistent obstructive lung disease. However, it has only been widely used by proponents of the Dutch Hypothesis, which states that these diseases all result from a common genetic root and should be considered as one disease. A major reason for proposing this hypothesis in 1961 was that these different entities share some common features, especially airway hyperresponsiveness. Although not formally disproven, evidence is accumulating--and reviewed here--against this "one disease concept"; hence, common features should not necessarily imply a common pathogenesis. Overlap features are sufficiently frequent in clinical practice to cause problems for labelling patients within the scope of CNSLD. The term could still be used as a starting point for a "splitting approach", identifying a small number of important basic features in order to allow a more systematic use of established labels for diseases within CNSLD. Our proposal for labelling emphasizes a consistent use of asthma, emphysema and chronic obstructive pulmonary disease (COPD), but restricts the use of chronic bronchitis to those patients with chronic bronchial hypersecretion without chronic airways obstruction.