Background: QT segment prolongation is a high risk factor for fatal arrhythmias. Several studies have indicated a possible relation between low testosterone levels and QT interval prolongation. Objectives: To compare the QT interval length in elderly patients with prostate carcinoma who were on anti-testosterone treatment and those who were not. Methods: We screened the electrocardiograms (ECGs) of 100 prostate cancer patients divided into two groups: 50 patients on anti-testosterone drug treatment and 50 patients not. QT interval length was measured according to the accepted methods. Results: The mean QTc 12 leads in the entire group was 0.45 +/- 0.04 sec, which is close to the upper limit. Mean QTc was actually longer in the control group and there was no QTc difference between the groups after adjustment for possible confounders. Prolonged QTc 12-lead ECG (48% in treated and 54% in non-treated) and lead L2 QT interval (50% in treated and 56% in non-treated) did not differ significantly between the groups. The analysis of QTc 12-lead ECG indicated no significant effects of anti-testosterone drug treatment. Only the use of furosemide was associated with QT prolongation. Conclusions: The results of this preliminary Study do not support our initial concern of an alarmingly prolonged QT interval in the anti-testosterone treated group. However, further prospectively designed studies are needed. In the meanwhile we call fora close follow-up of the QT interval length in patients receiving anti-testosterone treatment.