In this paper, a QoS-aware cross-layer scheduler for wireless LANs is introduced which allows the control of a number of data flows according to QoS requirements of the respective applications. It is based on a two-stage concept: The MAC layer scheduler uses an importance function to calculate the priority of a particular flow, whereas the PHY layer scheduler considers the channel conditions of a MIMO-TDMA transmission. It is shown that with the concept presented here, throughput and delay requirements of time-critical applications can be met.