Ankle sprains are a common musculoskeletal injury in sport. Older people are increasingly participating in sports such as running. The specificities of musculoskeletal injuries in older people pose a different diagnostic challenge from that in young people participating in the same activities. A clinical case is presented of a 64-year-old patient diagnosed with a grade 1, plantar flexion/inversion ankle sprain that was later diagnosed as a quite different and rare injury. Fractures of the fibular malleolus, talar neck and dome are possible differential diagnoses for an ankle sprain, as are talar dome chondral defects. Response to treatment may help to guide the diagnostic procedure when pain persists after appropriate treatment.