INTRODUCTION: Synovial cyst is a rare cause of compression neuropathy and its differential diagnosis can be misleading. PRESENTATION OF CASE: This article presents clinical, radiological, and histological findings of deep peroneal nerve palsy due to compression of a synovial cyst in a 30-year-old patient admitted with sudden drop foot. DISCUSSION: Focal nerve entrapment in lower extremity due to synovial cystis a rare entity. Differential diagnosis is important. Surgical excision is the main treatment method with high success rate. CONCLUSION: Synovial cyst compression which can be treated easily with surgical excision should be considered in rapidly progressed drop foot.