This report presents the case of a Japanese patient who developed Lyme disease. The patient was a 44-year-old woman who had general fatigue and the inability to open her mouth. She was initially suspected of having mild tetanus with lockjaw; however, she reported a past history of a tick bite while camping in the USA and had erythema migrans 2 months before this visit. Finally, Lyme disease was serologically confirmed. A few cases of Lyme disease are annually reported in Japan; however, this infectious disease should also be suspected.