The free fibula flap is now widely used in clinical applications for microvascular reconstruction and occasionally, to add bulk, the flexor hallucis longus (FHL) muscle is harvested along with the fibula. The post-operative morbidity is usually described as mild and temporary, however a reduction of hallux flexion is expected when muscle is harvested. This retrospective study assessed 32 patients, all of whom had undergone mandibular reconstruction with a free fibula flap between 1995 and 2009. All patients were assessed by a blinded observer using an average of three measurements of the range of motion of the metatarsophalangeal joint, the interphalangeal joint and the combined strength of the hallux flexors. It was found that the donor leg had a significant decrease in strength of hallux flexion independent of FHL muscle harvest. It is suggested that following the harvest of the fibula and its peroneal vessels, the muscle is possibly left devascularised and denervated. While the morbidity is small, it appears that no benefit is conveyed by FHL preservation.