We report the first likely known case of reactive arthritis caused by Haemophilus parainfluenzae. An 84-year-old woman developed polyarthritis of the neck, shoulders, and hips. Two months before admission, she had received dental treatment for caries; 1 week later, she noted fever and extremity pain. Physical examination revealed that the range of motion of both shoulders was limited to approximately 60°, in abduction and forward flexion, secondary to pain. Laboratory tests showed that the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and serum amyloid A (SAA) were 99 mm/h, 4.0 mg/dL, and 109.9 μg/mL, respectively.