We study a graph-theoretic approach to the H∞ performance of leader following consensus dynamics in the presence of external disturbances when the underlying graph is a directed network. We first provide graph-theoretic necessary and sufficient conditions for the consensus dynamics to have the system H∞ norm from external disturbances to the state of each agent to be lower than a certain value. Moreover, we discuss the tightness of the proposed conditions via examples. Then, we study the relation between the system H∞ norm for directed and undirected networks for specific classes of graphs, i.e., balanced digraphs and directed trees. Moreover, we investigate the effects of adding directed edges to a directed tree on the resulting system H∞ norm.