The present study examined the association between sleep duration and obesity in 40,834 middle-aged Australian adults. Multinomial logistic regression was used to test the relationship between sleep duration and obesity while controlling for important demographic and health covariates; separate models were tested for males and females. Short sleep (i.e., <7 h a night) was found to be independently associated with obesity in males and females. To our knowledge, this is the first study to report an association between short sleep and obesity in Australian adults. Although more research is required, interventions targeting short sleep could aid obesity treatment and prevention.