Objectives: The main aim of this work is to assess the level of knowledge about diabetes prevention and the consequences of untreated diabetes in the Polish society, as well as to indicate the variables that have a significant impact on that knowledge. Material and Methods: The analysis is based on the results of the National Multicenter Health Survey – WOBASZ II. The number of subjects surveyed was 6170, including 2760 men and 3410 women, aged 20–74 years. Data on socio-demographic variables, lifestyle and subjective health assessment were collected using the face-to-face technique. Results: The results obtained in the WOBASZ II project showed that >85% of the respondents had an unsatisfactory level of knowledge about diabetes prevention methods and approximately to 85% of the respondents – about the consequences of untreated diabetes. Moreover, one-fourth of the respondents were unable to identify a single way of preventing diabetes, and more than one-third could not identify a single disease caused by diabetes. The risk of a lack of knowledge about diabetes prevention and the consequences of untreated diabetes is more common for men, people with a low level of education, not married, non-diabetic, and without diagnosed diabetes in the family. Conclusions: The presented results indicate that there is an prevailing lack of knowledge about diabetes prevention and the consequences of untreated diabetes in the Polish society. It is associated with several variables like: sex, level of education, age, marital status, subjective health assessment and diabetes diagnosed in the respondent and/or in the respondent’s family. Int J Occup Med Environ Health. 2021;34(5):667–78