Only a few studies deal with electrocardiographic (ECG) signs of left ventricular hypertrophy (LVH) in patients with primary hyperaldosteronism, although it may be presumed that many factors such as arterial hypertension, hypokalemia, increased blood volume, and decreased activity of the renin-angiotensin system can modify LVH pattern in this entity. For that reason, we evaluated ECG signs of LVH in 55 patients with primary hyperaldosteronism hospitalized in our department from 1971 to 1990. These data were compared with age, serum potassium level, plasma renin activity (PRA) and-in 14 patients-with left ventricular mass, measured echocardiographically. We found inverse correlation between serum potassium concentration and the Sokolow-Lyon index: SV1 + RV5/6 (r = -0.47, p < 0.001). Among 24 patients with only abnormal QRS voltage, without ST-T changes suggestive of LVH, 19 (79.2%) had hypokalemia. In multivariate analysis, potassium concentration was the single independent predictor of an abnormal QRS voltage: -0.743, p = 0.01 vs. 0.153 (age), -0.337 (PRA) and 0.454 (LV mass). Our observations suggest that hypokalemia is an important factor influencing an amplitude of QRS complexes and may be responsible for false-positive LVH diagnosis.