Article dans une revue: This paper explores the relationship between ownership structure and firm value in firms listed on the Warsaw Stock Exchange. The results of the estimations, taking into account simultaneity and reverse causality, show that the relationship between ownership concentration and firm value differs across firms belonging to the sector of innovative technologies and more 'mature' firms. The results give support to the hypothesis that 'mature' firms with higher ownership concentration are likely to perform better than firms with more dispersed ownership. In contrast, in high-tech companies, with large share of knowledge related activities, higher ownership concentration is associated with lower firm value. This effect is robust to various alternative specifications.