Background: There are some risk factors being more vulnerable to Lemierre's syndrome such as a hypercoagulable state. Methods: We report a rare case of Lemierre's syndrome with ethmoid and maxillary sinusitis, bilateral mastoiditis, and sigmoid sinus thrombosis. Results: Genetic study revealed a double heterozygote status in the methylenetetrahydrofolate reductase gene including C677T and A1298C. Conclusion: It is suggested to screen patients with Lemierre's syndrome for a hypercoagulable state to consider anticoagulant therapy.