Purpose: "Just culture" is an element of safety culture, and in a broader sensea part of quality culture. It is the subject of studies, especially in healthcare. This phenomenon is almost unknown in Polish medical facilities. For this reason, the aim of the article is to present the essence and significance of "just culture" in healthcare. The other aim of the research is to present the results of the validation of "just culture" assessment instrument used to recognize the "just culture" maturity level and evaluate the nurses' beliefs and behaviours in the light of "just culture" criteria. Methodology/Approach: The verified questionnaire consisted of 28 statements in relation to which respondents expressed their opinion on a 5-point Likert scale. The questionnaire was distributed among nurses in one of the largest hospitals in Pomorskie Voivodship, in Poland. The results based on 68 responses were statistically processed with Statistica 13.1 software. Findings: The obtained results allowed to confirm the reliability of the assessment tool, to recognize the level of "just culture" as wisdom (68%) and to indicate strengths and weaknesses of observed beliefs and behaviours. On this basis, improvement actions were proposed. Originality/Value: We use the original, own prepared questionnaire. This is the first study on "just culture" in healthcare in Poland. There are only few studies devoted to patient safety culture in Poland and no research addressed to "just culture" phenomenon, as well in Poland as in Central Europe. The results in this area allow to recommend the assessment tool for other hospitals and seem to help in understanding the essence of "just culture" implementation.