OBJECTIVE: To estimate the prevalence of excessive daytime sleepiness (EDS) and its associated factors in a mixed population of employed Australian workers. METHODS: Study participants (n = 707) were volunteers from various Melbourne workplaces, participating in a workplace physical activity program in 2008. Daytime sleepiness was assessed using the Epworth Sleepiness Scale (ESS), with EDS defined as ESS scores >10. RESULTS: In this population of adult employees (40.0% male; mean age 40.2 ± 10.4 years), prevalence of EDS was 16.0%. Characteristics associated with EDS and higher ESS scores were age, higher body mass index, markers of poorer diet, and markers of poorer mental health. CONCLUSIONS: Excessive daytime sleepiness is potentially an important contributor to lower productivity and poorer mental health in the workplace. Our finding suggests that workplace health programs aimed at improving diet and body weight may also help alleviate EDS.