AbstractA 31‐year‐old woman developed low‐grade fever and pain and swelling of the masticatory muscles. A T2‐weighted magnetic resonance image showed high signal intensity in these muscles. Coxsackie B3 and echo 30 viruses were detected from a nasopharyngeal swab and feces, respectively. The clinical symptoms accompanied a marked decline in the serum immunoglobulin G level with progressive eosinophilia. Her symptoms disappeared by 8 weeks after onset. She was diagnosed as having masticator myopathy, which has rarely been reported in humans. The present case suggests that masticator myopathy is associated with coxsackie or echo virus infection. Muscle Nerve 28: 123–127, 2003