A woman in her 80s developed a feeling of abnormal sensation in her face and excessive salivation. She was diagnosed with right facial nerve paralysis and was admitted to a local hospital. On admission, serum creatinine level was 0.54mg/dL and estimated glomerular filtration rate was 79mL/min/1.73m2. She was started on oral valacyclovir at a dose of 3,000mg/day to treat the right facial nerve paralysis. However, 5 days after starting oral administration, she developed generalized fatigue, vertigo, and vomiting. Serum creatinine level rose to 4.99mg/dL with mild disturbance of consciousness, so she was transported to our hospital on suspicion of acyclovir-induced encephalopathy. We performed hemodialysis for 3 consecutive days to remove the acyclovir from the circulation, which subsequently improved all her symptoms. She was later diagnosed with allergic tubulointerstitial nephritis based on renal biopsy.After discharge from our hospital, laboratory data showed a serum creatinine level of 0.67mg/dL. We later confirmed that the serum acyclovir level before the first hemodialysis session had been very high (11.9μg/mL).