Isocyanates are extensively used for the production of different foams and elastomers. They also serve as glues, lacquer hardeners, inks, adhesives, fillers, finishes, sealants, coating and insulation materials. Usually, their application results in inhalative, partly also in cutaneous uptake. This review describes occupational exposures to isocyanates as well as hazardous effects. Isocyanates are used in the automotive/mechanical engineering/building and construction/mining/casting/electricity and electronic/plastics/printing/timber and furniture/white goods and textile industry, partly also in medicine. Hazardous exposures to thermal degradation products of isocyanate-based polyurethanes and other materials have also be taken into consideration. Obstructive airway diseases are the major disorder caused by isocyanates. Rare cases suffer from extrinsic allergic alveolitis or eczema. In addition to regulation-based primary prevention qualitative medical surveillance mostly prevents disorders. There is also a need for the establishment of a validated biomonitoring of endangered employees.