BACKGROUND: Many individuals may not accurately perceive whether their weight status poses a health risk. This paper aimed to determine how accurately Australians perceived their weight status compared to objective measurements, and to determine what factors were associated with underestimating weight status. METHODS: Participants were 7947 non-pregnant adults from the 2011 to 2012 Australian National Nutrition and Physical Activity Survey, with complete data for self-reported and measured weight status. Multivariate logistic regression was used to examine associations between individual characteristics and accuracy of perceived weight status. RESULTS: Overall, 25.5% of the sample underestimated and 3.8% overestimated their weight status. Men were almost twice as likely as women to underestimate (34.0% vs 17.7%, p<0.001). In both sexes, underestimating weight status was strongly associated with higher waist circumference, satisfaction with weight and older age. In men, underestimation was associated with low education levels and being on a diet, and in women, underestimating weight status was associated with being born overseas and area-level disadvantage. CONCLUSIONS: At least a quarter of the adult population misperceives their weight status as healthy when in fact they are at increased risk of morbidity and mortality due to overweight and obesity. This may present a major barrier to prevention efforts.