Evidence based on US firms suggests that large boards restrain risk taking. We investigate whether a similar effect exists in Japan. Our results confirm that firms with larger boards exhibit lower performance variability relative to firms with smaller boards. However, this effect is less significant when firms have plenty of investment opportunities, but considerably stronger when firms have few growth options. This new finding is consistent with recent evidence indicating that larger boards are not necessarily detrimental to firm performance. The results are shown to be robust to the endogeneity of board structure and the use of alternative risk measures and estimation methods.