Background and Objectives: The objectives of this study were to identify and validate a screening tool to detect malnutrition among Indigenous and non-Indigenous Australian patients. Methods and Study Design: This study included medical patients admitted into three regional hospitals in Australia. A literature review was undertaken of current screening tools before the Malnutrition Screening Tool (MST) and the newly developed Adult Nutrition Tool (ANT) were used to validate a screening tool for use among participants against the Subjective Global Assessment (SGA) tool. The sensitivity and specificity of both the MST and ANT were determined for all study participants as well as according to participants' Indigenous status. Results: A total of 608 participants were enrolled into the study, of whom 271 (44.6%) were Indigenous. The area under the curve (AUC) when utilising ANT was higher in all participants compared to the MST (0.90, 95% CI 0.88-0.92 versus 0.81, 95% CI 0.77-0.84, p＜0.001). The AUC was also significantly higher for Indigenous participants when utilising ANT compared to the MST (0.88, 95% CI 0.84-0.92 versus 0.78, 95% CI 0.73-0.83, p＜0.001). An ANT ≥2 demonstrated superior sensitivity for both Indigenous and non-Indigenous participants (96.0%, 95% CI 92.8-98.7%) than the MST (84.0%, 95% CI 78.9-88.3) but with inferior specificity (59.5%, 95% CI 54.2-64.6) than the MST (70.7%, 95% CI 65.7-75.3). Conclusions: The ANT is both a valid and accurate tool for Indigenous and non-Indigenous Australian patients. Further research is required to validate ANT to aide in the detection of malnutrition in other clinical settings.