The authors review the available data on occupational asthma in Italy; it is estimated that 500-600 cases occur per year, although it is difficult to establish the real prevalence of this disease; it is in any case under estimated. The author also reviews the medical/legal criteria used for diagnosis and compensation purposes, and criteria are proposed for the assessment of residual permanent damage. This assessment should be based not only on the degree of bronchial obstruction (as in the case of pneumoconiosis and chronic bronchitis), but also on the degree of bronchial hyper-reactivity and the need to take drugs (mainly steroid drugs orally). As examples, the author quotes the guidelines of the American Thoracic Society and the compensation system in force in Quebec in Canada, where these aspects are adequately taken into account. Assessment of residual permanent damage can only be performed when the clinical conditions of the patient, the spirometry and bronchial hyper-reactivity levels are stabilized (usually two years after cessation of exposure to the agent responsible for the disease); otherwise the damage may be overestimated or a false underestimation may result. The author stresses the importance of medical rehabilitation and retraining of the occupational asthmatic if resumption of his former job, which caused the disease, is not feasible. Early diagnosis of occupational asthma is necessary not only in order to avoid clinical aggravation of the disease but also to limit the social and economic costs.