Purpose: This paper aims to explore the topic of knowledge safety, defined as the state of knowledge being safe from loss, leakage, attrition, oblivion, waste or theft. The paper first presents a theoretical background and review of previous studies on knowledge loss and ways of overcoming it, and then illustrates the topic of knowledge safety with ten case studies from the small and medium-sized enterprises (SMEs) sector. Methodology: The paper is based on an analysis of Knowledge Management (KM) literature devoted to knowledge loss and its potential types in companies, and on the results of case study research. Knowledge safety was first defined and contrasted with other terms, and then examined in 10 selected SMEs. The research resulted in a clarification of what SMEs understand by the term of “knowledge safety” and what kind of measures they take to ensure it. Findings: As the analysis shows, the examined SMEs attribute diversified significance to the issue of knowledge safety. For some of them, such problem does not exist at all and they state that they can ensure knowledge safety in all aspects of their operations. Some companies perceive it mainly through the safety of the knowledge stored in electronic databases, while others link it with the human factor only. Research limitations: Research results are limited to ten companies operating in Poland. As such, they cannot illustrate the whole picture of the existing small or medium-sized companies. Research implications: The findings of both literature review and case study analysis indicate that there is a need to further examine the issue of knowledge safety by analysing the potential factors which may endanger knowledge safety and the methods to eliminate such risks. Practical implications: The paper examines important aspects of knowledge safety and provides guidelines on how it can be ensured by managers or owners of SMEs. Originality/value: The term of knowledge safety has been absent from the related literature so far. The paper defines it and explores both the theoretical and the practical aspects thereof. The paper also suggests further research possibilities in this area.