The circadian rhythm is an internal body cadence, responsible for regulation of sleep in all mammals. In humans, this clock is altered by several factors, including light and secretion of the hormone melatonin. Within the intensive care unit (ICU) population, it is well evidenced that patients suffer from circadian dysregulation, often for long periods of time. Additionally, many parallels have been noted between severely fragmented sleep and delirium, an acute neurological condition frequently observed in ICU patients. A prospective cohort pilot study of five subjects was undertaken to enable a greater understanding of both sleep in the ICU and the relationship between circadian rhythm and delirium. From a total of thirty-six urine samples per subject, excretion of 6-sulphatoxymelatonin (aMT6s), the urinary metabolite of melatonin was analyzed. T-test comparison (p=0.05) of mean aMT6s (ng/mL) revealed significant differences in the nighttime excretion between subjects in this study and healthy individuals. No significant differences were observed with t-test comparison of mean aMT6s of the first 24 hours from the current study to ICU subjects in previous literature. No subjects were identified as delirious in the study and therefore no relationship could be found between circadian rhythmicity, as evidenced by melatonin excretion and delirium in this study population. / February 2017