6 mmol/L) and treated with ACEI and spirolactone were included in this study. Patients were followed up for at least one month after admission. Results The mean age of the patients (9 males, 13 famales) was (72?11) years old. Four of them were diabetics. On admission, the serum potassium was (7.3?0.8) mmol/L and serum creatinine was (318.2?150.3) ?mol/L; these values were significantly higher than the most recent laboratory measurements (4.5?0.6) mmol/L and (159.1?114.9) ?mol/L, respectively obtained (11?4) weeks before admission. Out of these patients, 19 suffered from acute renal failure and the main causes were dehydration (n=11) and severe heart failure (n=8). The mean daily dosage of spironolactone was (48?27) mg. Among them 11 were concomitantly treated with other drugs that might cause hyperkalemia, and finally 1 patient died and 8 patients were treated by hemodialysis. Conclusions A combination treatment of ACEI and spironolactone should be considered with caution and serum potassium level should be monitored closely in patient with renal insufficiency, hyperkalemia, severe heart failure, diabetes, especially in those elder patients. Daily dosage of spironolactone should not be over 20 mg.