This paper presents a multithreaded software implementation of the Worldwide Interoperability for Microwave Access (WiMAX™) medium-access control (MAC) layer and its performance results on massively multithreaded (MMT) systems. The primary design goals of the implementation are to support the high WiMAX data rates, seamlessly scale with the number of available hardware threads, and provide per-flow guaranteed services. Our experimental results demonstrate that multithreading can be exploited to meet the high data rates of WiMAX and thus validate the IBM wire-speed processor MMT chip as a suitable platform for building WiMAX network appliances. The implementation consists of separate threads in the data and control planes, and thread coordination through concurrent data structures to enable multithreading in both the uplink and downlink data paths.