Sleep problems can lead to a bad quality of life and a raise of morbidity, also in dialysis patients. Sleep problems can be caused by a disturbance of circadian rhythms in our body. For a good regulation of these circadian rhythms a uniform external synchronisation is necessary. This is the synchronisation of the biological clock of our body by light and other influences. In case of a disturbance of the external synchronisation, due to for example naps during the day or wake periods at night, internal rhythms can be unlinked. As a result a weakened melatonin rhythm and a problematic sleep-wake cycle can be observed. Most dialysis patients have sleep problems. Their sleep latency is prolonged. They often take a nap during the day and their sleep efficiency is poor. There has only been one study on the melatonin rhythm of dialysis patients. The conclusion of this study was that the melatonin rhythm of dialysis patients is weakened and disturbed, probably caused by renal insufficiency. In this study no link was made between melatonin rhythm and the nature and severity of possible sleep problems. In different studies with non-dialysis patients and a disturbed melatonin rhythm, exogenous melatonin at the right time leads to a recovery of the normal rhythm and the normal biological clock and a better quality of life.