Since the introduction of the original IEEE 802.11 medium access mechanism, the definition of the multicast access mechanism has been the subject of numerous amendments and standardization efforts. Over the past few years, the need for a reliable multicast mechanism has been spurred due to the increasing demand for audio/video services. It is widely accepted that the success of any new multicast mechanism will mainly depend on its ability on meeting the stringent Quality-of-Service (QoS) requirements of the audio/video services. Due to the fact that the multicast service will have to be integrated into the IEEE 802.11 protocol architecture, it is essential to evaluate its performance in a scenario comprising unicast and multicast services. In this paper, we undertake the performance evaluation of a Multicast Collision Prevention (MCP) mechanism recently introduced in the literature. Our main goal is twofold: (1) to show that the MCP mechanism properly responds to the needs of multicast audio/video services in the presence of multicast/unicast traffic: a must for any new mechanism to be considered by the standards bodies; and (2) to provide simple guidelines on tuning-up the main system parameters of the MCP mechanism. Our numerical and simulation results also evaluate the impact of the MCP mechanism over the performance of the unicast service. Our findings show the overall benefits of the MCP in terms of the QoS metrics reported for the multicast service and the key performance indicators of the unicast traffic.