The authors found a serum sodium level of 113 mmol/l in a 70 year old confused male patient with cachexia and fever, which level rised to 125 mmol/l as a result of hypertonic sodium chloride and furosemide therapy, resulting in improving sensorium. At the same time the urine osmolality (235 mOsm/kg) was high compared to the serum osmolality (258 mOsm/kg). The physical and radiological examination showed bilateral pneumonia. The patient died in acute circulatory insufficiency. At the autopsy miliary pulmonary tuberculosis with superinfection by aspergillosis was proved. The authors discuss the possible mechanisms of water intoxication occurring with lung diseases and the difficulties regarding the diagnosis and therapy of aspergillosis.