The number occupational diseases reported is like the tip of an iceberg. Many occupational diseases are not recognized as such. A patient with occupational asthma has the same symptoms as any other patient with asthma. For asbestosis, there is a latency of at least ten years between exposure and disease. Medical students receive little training in the field of industrial toxicology. Finally, a large knowledge base is required to understand and diagnose work-related illnesses caused by chemicals and biological agents.