Late-onset asthma and occupational asthma may provide interesting models of human asthma to compare with the most frequent type of atopic early-onset asthma. The discovery of similarities and discrepancies in the aetiology and pathogenesis of these different diseases might provide new insights on different mechanisms producing the same phenotype and, thus, by recognizing the different underlying mechanisms of the different forms of asthma, may allow better targeting of prevention and treatment. Occupational asthma, in addition to being a late-onset asthma, provides the unique opportunity to study the development of asthma under measurable exposure conditions, and consequently to examine the effect of cessation of exposure which, at variance with allergen avoidance, is possible in most of the cases.