AIM: The disturbed circadian rhythm in haemodialysis patients results in perturbed sleep. Short term melatonin supplementation has alleviated these sleep problems. Our aim was to investigate the effects of long-term melatonin supplementation on quality of life and sleep. METHODS: In this randomized double-blind placebo-controlled trial haemodialysis patients suffering from subjective sleep problems received melatonin 3 mg day(-1) vs. placebo during 12 months. The primary endpoint quality of life parameter 'vitality' was measured with Medical Outcomes Study Short Form-36. Secondary outcomes were improvement of three sleep parameters measured by actigraphy and nighttime salivary melatonin concentrations. RESULTS: Sixty-seven patients were randomized. Forty-two patients completed the trial. With melatonin, no beneficial effect on vitality was seen. Other quality of life parameters showed both advantageous and disadvantageous effects of melatonin. Considering sleep, at 3 months sleep efficiency and actual sleep time had improved with melatonin compared with placebo on haemodialysis days (difference 7.6%, 95% CI 0.77, 14.4 and 49 min, 95% CI 2.1, 95.9, respectively). At 12 months none of the sleep parameters differed significantly from placebo. Melatonin salivary concentrations at 6 months had significantly increased in the melatonin group compared with the placebo group. CONCLUSIONS: The high drop-out rate limits the strength of our conclusions. However, although a previous study reported beneficial short term effects of melatonin on sleep in haemodialysis patients, in this long-term study the positive effects disappeared during follow up (6-12 months). Also the quality of life parameter, vitality, did not improve. Efforts should be made to elucidate the mechanism responsible for the loss of effect with chronic use.