This study was performed to evaluate whether any electrocardiogram (ECG) parameter can predict the presence of hyperkalemia in patients on maintenance hemodialysis (HD). In January 2006, we conducted a cross-sectional study of 80 stable patients with end-stage renal disease from four university-based HD units of Tehran, Iran, receiving conventional thrice-weekly HD. Pre-HD serum electrolyte values and conventional 12-lead ECG were obtained from each patient. Bivariate linear regression was used for assessing relationship of the study variables with hyperkalemia (K+ > 5.2 mg/dL). Multivariable logistic regression was used for evaluating independent relationship between decreased T wave duration (< or =170 ms) and other variables. Bivariate correlation analysis showed a significant inverse correlation between serum potassium concentration and T wave duration (P < 0.05). None of the patients with serum potassium of > or = 5.6 mg/dL had T wave duration >200 ms. Multivariate logistic analysis, after adjustment for other factors, also showed a significant relationship between decreased T wave duration (< or =170 ms) and hyperkalemia. We conclude that although hyperkalemia does not induce the usual ECG changes in HD patients, decreased T wave duration was found to be a good indicator of this lethal condition.