Purpose – The purpose of this paper is to determine whether there is a relationship among leadership, action, social, and personal competencies of managers in modern organizational structure types and whether a relationship exists between a company's organizational structure and performance. Design/methodology/approach – A questionnaire was carried out among top managers in Slovene mid- and large-sized companies. The relationship among managerial competencies, the choice of organizational structure type and the company effectiveness were measured with a value-added approach. The method of structural models was used for establishing the affect among individual variables. Findings – The results support the hypothesized effect of managerial competencies on a company's organizational structure type. The effect of a modern, horizontal organizational structure on a company's performance and growth on the market facilitates the achievement of higher value added as well as has a direct impact of managerial competencies on a company's performance. Research limitations/implications – The study was limited to mid- and large-sized companies in Slovenia. Only top managers were included in the study as they are the ones that are responsible and have the largest influence in creating a company's organizational structure. Practical implications – The paper includes implications to those organizations in the process of restructuring and for those companies that are prepared to modify traditional principles of management participation. Originality/value – To the authors knowledge no research studies were found that examined the affect and relation of top management competencies with respect to different organizational structures.