Purpose – This paper aims to investigate the relationship between ownership structure (ownership concentration and ownership composition) and firm performance in Kuwaiti non-financial firms. To this end, it examines the relationship between firm performance and ownership concentration to determine whether the impact of this relationship is conditional on the nature of the large shareholders. Design/methodology/approach – First, the relationship between ownership concentration and firm performance was tested using ordinary least squares regressions on 618 observations (103 listed firms) from 2005 to 2010; next, the ownership compositions were classified as institutional, government and individuals (families) and their impact on firm performance examined. Findings – The overall concentration ownership by large shareholders showed no impact on firm performance. However, when the type of shareholders was introduced, only the government and individuals (families) ownership categories influenced firm performance. Therefore, certain types of shareholders are better at monitoring, and not all concentration by large shareholders is beneficial to Kuwaiti firms. Research limitations/implications – This study examined only one important aspect of the corporate governance mechanisms, namely, ownership concentration. Thus, further study may include other mechanisms such as board variables, role of debt and shareholders rights in examining the firm performance. This study is limited to the Kuwaiti environment, and thus, next step can be very useful in case of comparing ownership concentration in the Gulf Cooperation Council (Kuwait, Bahrain, Qatar, Oman, United Arab Emirates and Saudi Arabia) or across different Arab countries. Practical implications – The results of this study have important implications for the regulators in Kuwait in their efforts to increase the efficiency of the rapidly developing capital markets and in protecting investors and keeping confidence in the economy. They may mandate a corporate governance code to protect minority shareholders. Investors may use the findings to understand Kuwaiti companies. Such findings may assist them to diversify their investment portfolios. Originality/value – This paper extends literature review by investigating the role of large shareholders in the context of a developing country that is characterized by high level of ownership concentration and weak legal protection for investors as well as the absence of code that organized the corporate governance practices.