An carcinogen is an agent that is directly involved in the formation and development of a malignant tumor or cancer. Carcinogenic substances are substances that, under certain circumstances, can cause malignant transformation of cells. According to OSHA - Occupational Safety and Health Administration, an occupational carcinogen is any substance or combination of certain substances that causes an increase in the incidence of cancer or significantly shortens the latent period between exposure and the onset of cancer. Professional carcinogens are divided into 3 groups: chemical, physical and biological carcinogens. Laws, directives and regulations of the European Union and the Republic of Croatia prescribe and determine the rules for dealing with carcinogenic substances and the protection of employees at the workplace. Employers have an important role in protecting workers from the effects of carcinogenic substances in the workplace, who must comply with laws and regulations in order to reduce the risk of occupational cancers among workers to a minimum level. Occupational cancers are diseases caused by carcinogenic substances with which the worker was in contact at the workplace, where lung cancer is mentioned as the most common type of cancer, followed by sinus, nose and larynx cancer, skin cancer, bladder cancer, cancer of the liver and blood-forming organs. All occupational malignant diseases can be prevented. The most effective way is to completely remove harmful agents and industrial processes from the work environment or replace them with other agents that do not cause malignant tumors. It should be insisted on the maximum lowering of concentrations and/or length of exposure to carcinogenic agents with regular measurement of exposure.