Introduction Heart rate variability (HRV) provides information about autonomic nervous system function, and has been shown to vary across the sleep-wake cycle. Measures of HRV have also been found disturbed in sleep disorders such as sleep apnea and insomnia. However, it remains unclear whether HRV could be used as a biomarker of sleep quality. Here we evaluated the association between HRV and sleep efficiency in a group of healthy volunteers. Materials and methods 39 (9 men) young university students with a mean age of 23.85 (SD=6.92) completed a psychological distress questionnaire (Depression Anxiety Stress Scale, DASS), and a sleep diary for seven consecutive days. At the end of the daily diary period, participants completed a laboratory visit between 9 AM and 12 PM. During the visit, participants wore a digital interbeat interval recorder (Polar 800CX) and were instructed to relax as they remained seated during 7min. Average sleep efficiency (time asleep/time in bed) over one week was computed for each participant from the aggregated sleep diary data. The HRV parameters rMSSD, pNN50, and Respiratory Sinus Arrhythmia (RSA) were extracted using Kubios HRV (version 2.1, University of Eastern Finland) and CardioBatch (University of Illinois at Chicago). The association between HRV parameters and sleep efficiency was tested by Pearson correlations and linear regressions on log-transformed variables. Results rMSSD, r=.44 p=.007, pNN50, r=.50 p=.002, and RSA, r=.45 p=.005, were positively correlated with average sleep efficiency. In hierarchical regressions, rMSSD, p=.01, pNN50, p=.002, and RSA, p=.005, predicted sleep efficiency over and above differences in age, sex, ethnicity, and current psychological distress. Conclusion Greater HRV during resting wakefulness is associated with better sleep efficiency measured with sleep diaries over one-week period in healthy young individuals. This relationship remains significant after taking into account demographic and psychological variables. Therefore our results indicate that HRV during a short resting period is an independent index of sleep efficiency, and could be used as a clinical biomarker of sleep quality. Future studies should reassess this relationship in various clinical populations. Acknowledgements Support from the Canadian Institutes of Health Research (CIHR), the Natural Sciences and Engineering Research Council of Canada (NSERC), the Fonds de Recherche du Québec – Santé (FRQS), the Sleep Research Society Foundation (SRSF), and the Petro-Canada Young Innovators Awards Program.