BACKGROUND AND AIMS In the last few years there has been active interest in the study of QT interval dispersion (QT-d) calculated from the 12-lead ECG, as a non-invasive method of investigating the homogeneity of ventricular recovery time. The aim of this study was to evaluate QT interval dispersion, analyzing in particular gender and age relationships. Discussion of its electrophysiologic and clinic meaning is still open; moreover, the method must be standardized and normal values should be clearly defined. METHODS The two common indices, range and standard deviation of QT, were taken into account. The study sample is part of the population-based Italian Longitudinal Study on Aging (ILSA) with individuals older than 64 years. Three groups were identified by clinical data: 256 healthy subjects, 98 patients with only cardiac diseases, and 472 patients with only hypertension. RESULTS Age (< 75 and > 75) and gender subgroups were considered, showing that age and gender influence the QT-d differently in the three groups. QT-d indices were influenced in the healthy group by gender (p < 0.001), in the cardiopathy group by age (p < 0.001), and in the hypertension group by age (p < 0.02) and gender (p < 0.01). Then the two gender groups were considered separately. In the female group, QT-d increased significantly with age only in the healthy group (p < 0.02), whereas in the male group it increased significantly in the cardiopathy and hypertension groups (p < 0.01). CONCLUSIONS The two QT-d indices behaved in a very similar way in all the comparisons. In older people, gender and age influenced the three clinical selected groups differently. However, it was shown that is not possible to indicate a clear, definite threshold value classifying with accuracy a single subject in the clinical groups; and a clear-cut, direct clinic application is still doubtful.