Cigarette smoking is a known risk factor for many chronic illnesses such as coronary heart and chronic obstructive pulmonary diseases. Smoking is often described as a risk factor for occupational asthma even though its effect on the development of asthma is still under debate and the links between smoking and occupational asthma, occupational rhinitis or occupational sensitization are elusive, controversial and contradictory. This review describes these relationships in a wide range of occupations, from laboratory, farm, brewery and hospital workers, to bakers, printers, cleaners, fish processors and others as observed in cross-sectional, cohort, and case-control studies published over the past thirty-five years i.e. from 1970 to 2005. Surprisingly, the data show there is little to support the view that the risk of occupational asthma is increased in workers who are smokers. However, evidence emerges of an increased risk of occupational sensitization in smoking workers exposed to several high and low molecular weight agents. This in-depth review confirms the relationship between smoking and occupational asthma is complex and contradictory. It deserves more attention and further studies, which need to be conducted without being influenced by selection bias or by the justifiable prejudice against smoking.