OBJECTIVE: To collect data and determine the degree of industrial concentration in the insurance market of Croatia, Slovenia and Hungary in the period from 2017 to 2021 using the concentration ratios CR4 and CR8, the Hirschman-Herfindahl index and the entropy index. METHODS: Using the market shares of the insurance companies of the observed countries calculated on the basis of their total gross written premium, relevant indicators of the degree of concentration will be applied, such as the concentration ratio of the four leading companies on the market (CR4), the concentration ratio of the eight leading companies on the market (CR8), the Herfindahl-Hirschman index (HHI) and the entropy index (E). RESULTS: In the insurance markets of the observed countries, an increase in the degree of concentration was recorded in the period covered by the analysis. The highest degree of concentration is recorded in Slovenia, whose insurance market is moderately concentrated and belongs to the market structure of a firm oligopoly. The Croatian and Hungarian insurance market is characterized with low degree of concentration. CONCLUSION: Mergers and acquisitions carried out by insurance companies in order to strengthen their market position influenced the dynamics of the level of concentration, and the recorded increase in concentration in certain years can be primarily explained by the merger and acquisition activities carried out. Despite the increase in concentration, the Croatian and Hungarian insurance markets, unlike the Slovenian one, are low concentrated and their market shares are more evenly distributed.