We report here an 83-year-old woman presenting with somnolence possibly induced by indapamide. She was diagnosed as having hypertension (180/110 mmHg), and 1 mg/day of indapamide was administered starting in October, 2002. Two months later, she complained of nausea, vomiting, and appetite loss and frequently fell down. On admission, she was hypotensive (90/54 mmHg). Neurologically, she was in a somnolent state (Japan Coma Scale 2-20), and showed brisk deep tendon reflexes of both upper limbs with bilateral Chaddock signs. Laboratory examination showed severe hyponatremia (115 mEq/l) and hypokalaemia (2.8 mEq/l). On brain MR imaging, there were no remarkable abnormalities, except for multiple lacunar infarctions. After the administration of indapamide was discontinued, her consciousness level and serum electrolytes immediately returned to normal levels. After a good effect for stroke prevention was reported, indapamide was widely prescribed in combination with angiotensin-converting enzyme (ACE) inhibitors, or angiotensin II receptor blocker (ARB) among the neurologists. We should keep in mind the risk of hyponatremia and hypokalaemia occurring in patients receiving indapamide, especially elderly women.