 The aim of this placebo controlled study was to investigate the effect of 2 mg Melatonin Slow Release Circadin on the sleepwake cycle in elderly insomniac out-subjects, aged 55 years or more. Sleep was assessed by means of polysomnography hypnographic results, all-night sleep EEG spectral analysis functional and quantitative results of sleep EEG, actimetry SomnitorTM, wake EEG and sleepwake quality questionnaires. Vigilance and cognitive skills were assessed by means of psychomotor and neurocognitive tests derived from the Leeds psychomotor test battery vigilance and arousal and TEA battery attention. 