Unlike single omnidirectional antennas, multiple antennas offer wireless ad-hoc networks potential increases in their achievable throughput and capacity. Due to recent advances in antenna technology, it is now affordable to build wireless devices with more than one antenna. As a result, multiple antennas are expected to be an essential part of next-generation wireless networks to support the rapidly emerging multimedia applications characterized by their high and diverse QoS needs. This paper develops an admission control framework that exploits the benefits of multiple antennas to better support applications with QoS requirements in wireless ad-hoc networks. The developed theory provides wireless ad-hoc networks with flow-level admission control capabilities while accounting for cross-layer effects between the PHY and the MAC layers. Based on the developed theory, we propose a mechanism that multiple antenna equipped nodes can use to control flows' admissibility into the network. Through simulation studies, we show that the proposed mechanism results in high flow acceptance rates and high network throughput utilization.