This paper explores the relation between ownership structure, board composition and firm performance among Swedish listed firms. The descriptive statistics show that Swedish board of directors have become more diversified in terms of gender. The analysis show that board size has a significant negative effect on investment performance. Gender diversity has a small but negative effect on investment performance, and the same holds for CEO being on the board. When incorporating all the explanatory variables into the same equation the negative effect of larger boards dilutes the effect of gender diversity and having the CEO on the board.