BACKGROUND: About 30% of women experience severe continuous low-back pain in labour, but limited options are available to reduce this pain especially in developing countries and remote areas. AIMS: To evaluate the efficacy of subcutaneous sterile water injection in reduction of labour pain compared with placebo. METHODS: One hundred (100) consecutive patients were enrolled in a double-blind randomised controlled trial. During the first stage of labour with planned normal vaginal delivery, the intervention group (n = 50) received 0.5 mL sterile water injected subcutaneously and the control group (n = 50) received normal saline as a placebo. Pain score was measured before and 10 and 45 min after the injection, using the faces rating scale. MAIN OUTCOME MEASURE: Low-back labour pain. RESULTS: The two groups were not significantly different regarding maternal age and weight, gestational age, parity and gravidity and degree of effacement. The median pain score was equal in both groups prior to the injection. Pain severity was reduced in both groups after the injection. However, the median pain score in the sterile water group was significantly lower than the placebo group 10 min (P < 0.01), as well as 45 min, after the injection (P < 0.01). CONCLUSION: Administering one subcutaneous injection of sterile water in a painful point of the lumbosacral area is effective in reducing low-back pain during labour.