The so-called 'Dutch hypothesis' (Fletcher) which describes chronic obstructive (restrictive) pulmonary disease (CO(R)PD) as a consequence of complicated childhood asthma (from 1900-1960) is well-founded. It can explain many aspects of the ever changing pattern of asthma and COPD in the Western world. Severe respiratory disease in children during the first part of the 20th century was primarily the result of respiratory complications of measles and whooping cough, and caused a high mortality in children below the age of two years. Gradually more children survived and a picture of the complications was formed: chronic bronchitis and bronchiectasis. In 1939 it was suggested that this happened mainly in children with asthmatic predisposition and this pattern was documented in detail in the post World War II period. After 1970 the complications virtually disappeared as a result of vaccination and improved therapy. Consequently, bronchiectasis and cor pulmonale became rare and CO(R)PD became COPD, the old-age form of asthma. There has also been a marked increase in asthma after childhood over the past 30 years. The double role of obstruction-provoking and anti-obstructive (and asthma-masking) infections plays an important role in this respect. The old picture from the fifties in the Western world still prevails in developing countries. Prevention of this 'old COPD' must consist of vaccination against measles and whooping cough (and possibly also against respiratory syncytial virus), and treatment of asthma.