OBJECTIVE: To examine the relationship between perceived body weight and measured Body Mass Index (BMI) among urban Aboriginal Australian adults. METHODS: We compared responses to a question on perceived weight with BMI based on measured health and weight among 248 Aboriginal volunteers aged>or=15 years who took part in a larger health study in the Darwin area between September 2003 and March 2004. Logistic regression was used to examine associations between socio-economic, demographic and cultural factors and under-assessment of weight. RESULTS: Being male and having diabetes were significantly associated with under-assessment of weight. Despite under-assessment being common, most participants with a BMI>or=25--and almost all (>90%) those with BMI>or=25 plus high waist circumference--described themselves as overweight. CONCLUSIONS: Study participants with BMI>or=25 were generally able to classify themselves appropriately as overweight. IMPLICATIONS: Lack of awareness of weight is unlikely to represent a major barrier to engaging Aboriginal people. However, other barriers exist, and both individual-level and environmental/structural approaches are required to reduce the burden of obesity among Aboriginal Australians.