Objective: Short (< 7 h) and long sleep durations (≥ 9 h) have recently been linked with increased mortality in the US, Europe and Asia, but little is known about the sleep patterns of Australian adults. The present study examined the sleep habits of Australian adults and identified socio-demographic and health-related factors associated with short and long sleep. Methods: This study analyzed cross-sectional and self-reported data from 49,405 Australian adults aged 45 to 65 years collected between 2006 and 2008. Socio-demographic and health-related factors were entered into multinomial logistic regression models predicting self-reported sleep duration. Results: Short and long sleep were reported by 16.6% and 13.9% of participants respectively. Short sleep was associated with long working hours (odds ratio [OR] = 1.17, 95% confidence interval (CI): 1.08, 1.28) and obesity (OR = 1.29, 95% CI: 1.19, 1.41); long sleep was associated with recent treatment for cancer (OR = 1.64, 95% CI: 1.34, 2.02) and heart attack/angina (OR = 1.58, 95% CI: 1.19, 2.09). Conclusions: Short and long sleep were common in this sample of middle aged Australian adults. The determinants of short sleep have potential public health implications and could be targeted to prevent morbidity and mortality associated with short sleep.