Background and objective: Spontaneous atraumatic bilateral Achilles tendon tears are very rare. The most common risk factors for sudden bilateral Achilles tendon tears have been attributed to prolonged corticosteroid use. This study aimed to present the efficiency of surgical reconstruction of bilateral flexor hallucis longus graft on spontaneous atraumatic bilateral Achilles tendon tear. Subject and methods: This study reported a 25-year-old male who suffered from spontaneous atraumatic bilateral Achilles tendon tear. The patient was surgically managed by surgical reconstruction of bilateral flexor hallucis longus graft and immobilised with above knee cast in plantarflexion for six weeks. The patient was then subjected to physiotherapy at 6 weeks after surgery. This study was approved by the Institutional Review Board of Jagadguru Sri Shivarathreeshwara Hospital, India. Results: Flexor strength at the time of removal of the cast was 3/5. After graded physiotherapy targeted at calf strengthening, flexor strength improved to 4/5. At the end of one-year follow-up, foot function recovered well. The Leppilahti score was recorded to be 78 for the right calf and 76 for the left calf at the last follow-up. Conclusion: Idiopathic spontaneous bilateral Achilles tendon tear was successfully managed by surgical reconstruction of flexor hallucis longus graft.