BACKGROUND: Breast-feeding in the postpartum period is known to induce intense uterine contractions with pain in the lower abdomen. AIMS: The primary aim of this study was to compare the effects of high and low intensity, high frequency Transcutaneous Electric Nerve Stimulation (TENS) on pain and discomfort of postpartum uterine contractions. The secondary aim was to evaluate discomfort experienced from the stimulation itself. METHODS: Twenty-one newly delivered women participated in this single-blind trial, 12 women received high intensity, high-frequency TENS (HI TENS) and 9 women received low intensity, high-frequency TENS (LI TENS). The electrodes were placed abdominally on each side of the uterus. Stimulation was done during one minute. Visual analogue scales were used to evaluate the intensity of the pain before and after stimulation. A verbal scale was used to estimate sensation of discomfort before, during and after stimulation. RESULTS: The median decrease in pain ratings before and after treatment by VAS was larger in the HI TENS group -49 mm (95% CI -66.5--33.2) than in the LI TENS group -21 mm (95% CI -39.0--20.0). The reduction of pain was most pronounced in the HI TENS group (median difference 28 (95% CI was 14.0-53.0). Furthermore, the HI TENS group experienced significantly less discomfort of the uterine contractions after stimulation (p