A 75-year-old man presented with hemoptysis. Consolidation was identified in the left lower lobe around multiple bullae. He was found to have chronic necrotizing pulmonary aspergillosis based on a high titer of aspergillus antigen and positive antibody. He was treated with 400 mg/day voriconazole. However, liver dysfunction and hyponatremia developed at 21 days after beginning administration of voriconazole. Serum sodium levels were 122 mEq/l. but urinary sodium showed a high level of 135 mEq/l. The serum sodium level improved 10 days after voriconazole was discontinued. Serum levels of voriconazole on day 15 were high at 18 μg/ml (safe effective serum level: 1.5 to 4.5 μg/ml). An analysis of genetic polymorphism showed a mutation of cytochrome P450 (CYP2C19*2G681A). We report the first case of a voriconazole-induced syndrome of inappropriate antidiuretic hormone caused by a polymorphism mutation of cytochrome P450.