Background: The aim of the study was to assess the biological risks of medical laboratory employees with particular focus on laboratory acquired infection (LAI), activities having the greatest risk, accidents with biological material, post exposure procedure, preventive measures and workers' knowledge about biological exposure. Materials and Methods: The study involved 9 laboratories. A questionnaire survey was attended by 123 employees and 9 heads of these units with the use of two questionnaires for laboratory workers and the managers. Results: 32.5% of the respondents (40 persons) had an accident at least once. Needlestick or a broken glass injury covered 18.7% respondents (23 persons), while splashing the skin, mucous membranes or conjunctivae related to 22.8% (28 persons). Among the employees who had an accident, only 45% of the respondents (18 persons) reported this to the manager. Microbes dominant in the biological material were known only to 57 respondents (46.3%), less than half could correctly give an example of a disease (57 persons, 46.3%). More than half of the respondents admitted that they do not know all of the possible routes of infection while working in the laboratory (68 persons, 55.3%). Conclusions: In the study population, a high incidence of accidents was observed, usually during blood sampling and transfer of biological material. Condition of the workers' equipment with personal protective measures and laboratory facilities in devices to reduce the risk of infection and procedures for handling the potentially infectious material should be considered as insufficient. Lack of basic knowledge of the employees about biohazards at workplaces was shown. Med Pr 2013;64(4):473–486