While the English literacy outcomes of Aboriginal children are constantly measured and debated, attention falls away once they leave school, leading to limited data on English literacy rates among Australia's Aboriginal adults. This paper reports on an investigation into the prevalence of low literacy in adults in eight Aboriginal communities in NSW, Australia, drawing on both self-report data from household surveys and objective professional assessments using the Australian Core Skills Framework (ACSF). The research was conducted in partnership with a national Aboriginal organisation as part of a longitudinal study of the impact of improved adult literacy on the social determinants of health and social wellbeing. Of the participants who were measured to have low or very low English-language literacy level using ACSF, 51% had completed Year 10 or higher. This casts serious doubt on the value of school completion data which is used, for example, in Close the Gap reporting, as an accurate predictor of adult literacy rates. Results further show that while self-reported low literacy was prevalent in the population studied, there was also a significant overestimation, with adults who have completed years 10-11 nearly 30 times more likely to overestimate compared to people who only complete primary school. Given the well-known associations between adult literacy and a range of other outcomes including income, employment and health, national adult literacy surveys such as the Program for International Assessment of Adult Competencies should aim to produce more comprehensive national, regional and local data on Aboriginal adult English literacy.