Genetic aberrations play a major role in human disease. They are responsible for a number of birth defects and have been identified as an important cause of much prenatal mortality. Approximately one-half of all conceptuses, for example, have been estimated not to survive to term, and some die so early that they are not even detected by the mother. Not all genetic anomalies appear at birth, however, since a number may result postnatally from environmental agents that have caused single cell mutations (which might develop into a human tumor), and yet others may require a second mutational event and appear even later. Thus, the industrial environment poses special hazards, to both female and male workers, because of the risks of induction of cancer, as well as of impairment of reproductive ability. Industrial cytogenetic monitoring, as a form of preventive medicine, is now possible. This review discusses many of the causes and types of genetic damage and the current cytogenetic techniques, as well as their use in industrial monitoring.