A cooperative multichannel directional medium access control (CMDMAC) protocol incorporating minor-lobe interference is proposed for directional ad hoc networks. While most existing MAC protocols require either extra equipment or clock synchronization to address deafness and directional hidden terminal problems, CMDMAC requires neither to solve these problems. Observing that directional transmission assumes single data channel in most instances, CMDMAC incorporates directional and multichannel transmissions to deliver superior networking performance. Theoretical analysis for CMDMAC is provided, and its performance is validated via NS-2 simulation. We compare CMDMAC with a noncooperative version, which is called NCDMAC, and observe a throughput improvement of around 15% and 56% in the single-data-channel and multiple-data-channel scenarios, respectively. We examine CMDMAC under mobile scenarios and observe throughput degradations of around 11% and 15% compared with the static single-data-channel and multiple-data-channel scenarios, respectively. We also compare CMDMAC with other popular directional and multichannel MAC protocols, and the results show that CMDMAC outperforms all of them.