Vitamin D deficiency (serum 25-hydroxyvitamin D (25(OH)D) concentration <50 nmol/L) is recognised as a public health problem globally. This study details the prevalence of vitamin D deficiency in a nationally-representative sample of Australian Aboriginal and Torres Strait Islander adults aged ≥18 years, and identifies demographic and lifestyle factors associated with vitamin D deficiency. We used data from the 2012-13 Australian Aboriginal and Torres Strait Islander Health Survey (AATSIHS). Serum 25(OH)D concentrations were measured by liquid chromatography-tandem mass spectrometry. Survey-weighted characteristics of participants, stratified by sex, were summarised using numbers and proportions (n=3,250). Survey-weighted logistic regression models were used to determine the independent predictors of vitamin D deficiency. Approximately 27% of adult AATSIHS participants were vitamin D deficient. The prevalence of vitamin D deficiency was 39% in remote areas, compared with 23% in non-remote areas. Independent predictors of vitamin D deficiency included assessment during winter (men, adjusted odds ratio (aOR):5.7; 95% confidence interval (CI):2.2,14.6; women, aOR:2.2; 95% CI:1.3,3.8) and spring (men, aOR:3.3; 95% CI:1.4,7.5; women, aOR:2.6; 95% CI:1.5,4.5) compared with summer, and obesity (men, aOR:2.6; 95% CI:1.2,5.4; women, aOR:4.3; 95% CI:2.8,6.8) compared with healthy weight. Statistically significant associations were also evident for current smokers (men only, aOR:2.0; 95% CI:1.2,3.4), remote-dwelling persons (women only, aOR:2.0; 95% CI:1.4,2.9) and university-educated persons (women only, aOR:2.4; 95% CI:1.2,4.8). Given the high prevalence of vitamin D deficiency among Aboriginal and Torres Strait Islander adults, there is a need to develop and promote strategies to maintain adequate vitamin D status through safe sun exposure and dietary approaches.