Ankle sprains are a common injury. According to the National Electronic Injury Surveillance System (NEISS), an estimated 630,891 ankle sprains occurred in 2009 (CPSC, 2011). The anterior talofibular ligament (AFTL) is frequently sprained as a result of a plantarflexion-inversion injury. Sometimes the calcaneofibular ligament or posterior talofibular ligament (PTFL) is also sprained (Komenda and Ferkel, 1999). The patient in this study presented with lateral ankle pain reproducible by passive plantarflexion and eversion, complaining of pain during exercise and playing sports. These findings are consistent with a sprain of the PTFL. Positional faults have also been shown to occur at tibiofibular joint, mimicking the symptoms of an ankle sprain. Brian Mulligan first hypothesized the occurrence of positional faults at the ankle. He developed a Mobilization with Movement (MWM) technique to treat these positional faults. Mulligan also hypothesized that a similar positional fault could occur in a posterior direction mimicking a sprain of the PTFL (Mulligan, 2010, p. 71, 96-97). The purpose of this case study is to present a patient with an apparent posterior talofibular ligament sprain who responded to an anterior glide MWM of the fibula. The two measurements used to assess function and pain were the Foot and Ankle Ability Measure (FAAM) and a 10-point numeric pain scale. Each measure was conducted prior to treatment, after treatment was discontinued, 6 months post treatment and 12 months post treatment. A positive response was achieved, as her symptoms were reduced and she was able return to her prior level of function.