Occupational asthma (OA) is one of the most common forms of occupational lung disease in many industrialized countries, having been implicated in 9 to 15% of adult-onset asthma. Work-related asthma includes: 1. immunologic OA, characterized by a latency period before the onset of symptoms; 2. nonimmunologic OA, which occurs after single or multiple exposures to high concentrations of irritants; 3. work-aggravated asthma, which is pre-existing or concurrent asthma exacerbated by workplace exposures; and 4. variant syndromes. OA is important to recognize clinically, because it has serious medical and socioeconomic consequences. Diagnosis of OA should be confirmed by objective testing early after its onset. Removal of the worker from exposure to the causal agent and early treatment with anti-inflammatory drugs lead to a better outcome. Assessment of the work environment and identification of host factors may provide us with useful information about the mechanisms involved in OA. Another issue concerns strategies for preventing OA which should be implemented.