Purpose: One of the main contributors to proximal fifth metatarsal fracture is ankle inversion and the incidence of recurrence may increase in patients with ankle instability. So, the authors confirmed the patients of proximal fifth metatarsal fracture with ankle instability by checking the history and magnetic resonance imaging (MRI) and assessed the value of MRI as therapeutic prognosis and clinical indicators for prevention of recurrence. Materials and Methods: Patients with proximal fifth metatarsal fractures visited our hospital during recent five years were reviewed. 35 patients with suspected damage by ankle inversion had been identified a history of ankle instability and checked the hindfoot malalignment through hindfoot alignment view and MRI was performed prospectively. The patients was devided to three groups on the location of fracture site and the groups were compared each other. Results: The mean time from injury to checking MRI was 10.7 days. There was no structural abnormality and was no significant difference according to the location of fracture. The patients with history of ankle inversion were 31(88.6%) and the patients with history of chronic or recurrent injury were 22 patients (62.9%). The lesion of MRI related to lateral ankle instability were identified in all patients. Conclusion: This study noted a high incidence of lateral ankle instability that was identified by MRI in the patients of proximal fifth metatarsal fracture. Aggressive treatment for lateral ankle instability should be needed for complications as proximal fifth metatarsal fracture to reduce the recurrence and occurrence.