In this paper, we analyze the outage probability and average throughput of opportunistic relaying with ARQ when the outdated channel state information (CSI) is available for relay selection. Its diversity order is analyzed to show that it is determined by the number of relays and the maximum number of ARQ rounds. Numerical results verify our analysis by comparison with computer simulation and show the effect of outdated CSI on its outage probability, diversity order, and average throughput.