In 2004, the category of formaldehyde carcinogenicity was changed in Poland so that it is now coherent with the requirements of the European Union classification of carcinogenicity. Formaldehyde was categorized into group 3 as the substance not classifiable as to its carcinogenecity to humans because the collected information was not adequate for making a satisfactory assessment. There is some evidence from appropriate animal studies, but it is insufficient to categorize this substance in group 2: probably carcinogenic to humans. In 2006, the International Agency for Research on Cancer categorized formaldehyde in group 1 as the substance carcinogenic to humans. Three types of cancer were assessed: nasopharyngeal cancer, leukemia and sinonasal cancer. There was sufficient evidence that formaldehyde causes nasopharyngeal cancer, strong but not sufficient evidence that the substance induces leukemia and limited evidence for sinonasal cancer. Based on the irritation effect, the value of maximum admissible concentration of formaldehyde in the work environment has been established in Poland at 0.5 mg/m3 as average weighed concentration, and 1 mg/m3 as short-term concentration. In the European Union, the values of 0.2 mg/m3 and 0.5 mg/m3, respectively are now being considered. It is assumed that the MAC value for formaldehyde in the work environment will be soon verified in Poland and adapted to European Union standards. Med Pr 2007;58(6):527-539