Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. In IEEE 802.11 wireless LANs, multicast is specified as a simple mechanism that does not make use of ACK frames. The absence of a feedback mechanism has a strong impact on the reliability of the service provided to the user. This is particular true in a network composed of a large number of active stations due to the increasing number of collisions. This situation has led many researchers to design techniques aimed at improving the reliability of the multicasting mechanism. However, the IEEE has created a Working Group to define the IEEE 802.11aa amendment. The first IEEE 802.11aa draft defines the mechanisms for wireless LANs which aim to provide a reliable multicasting. In this paper, we introduce a novel mechanism, capable of sending multicast data packets without collisions. Our scheme has been designed to maintain compatibility with the IEEE 802.11 standard. Our simulation results show that our new scheme outperforms the IEEE 802.11, and the most relevant ones reported in the literature.