Asthma affects 5-10% of people worldwide. The incidence of occupational asthma in adults is unknown. In the United States, it has been estimated to be 15% of all asthma patients. The two categories of asthma in the workplace are occupational asthma and work-related asthma. The former is characterized by variable airflow limitation, bronchial hyperresponsiveness, or both, due to conditions in a particular work setting, and the latter by preexisting asthma which is aggravated in the workplace. Occupational asthma with latency is caused by a broad spectrum of natural and synthetic materials which are subdivided into IgE-dependent and IgE-independent agents. In general, IgE-dependent agents include isolated early reactions or biphasic reactions, and IgE-independent agents induce late, biphasic, or atypical asthmatic reactions. Pathologic airway changes are similar to those in patients with other forms of asthma. Occupational asthma without latency (irritant induced asthma) differs from the former by fibrosis of the bronchial wall and fewer T lymphocytes, suggesting the absence of immunologic mechanism. Exposure is the most important determinant. Previous history of atopy and smoking are contributory factors in the IgE-dependent variety. The duration of symptoms before removal from exposure is a prognostic indicator. Diagnosis is based on compatible history and presence of bronchial hyperresponsiveness or variable airflow limitation by objective methods. An occupational cause should be sought for all asthma of new onset in adults. Early referral is essential, and the ideal management for patients with occupational asthma with latency is removal from exposure. Pharmacologic treatment is similar to other forms of asthma. The author suggests that because of the constant introduction of new chemicals into workplaces and the potential for disability, the economic consequences of occupational lung disease are considerable, hence more research and prevention are priorities in the next decade.