OBJECTIVES:To determine the validity, sensitivity, specificity and acceptability of the culturally adapted nine-item Patient Health Questionnaire (aPHQ-9) as a screening tool for depression in Aboriginal and Torres Strait Islander people. DESIGN:Prospective observational validation study, 25 March 2015 - 2 November 2016. SETTING, PARTICIPANTS:500 adults (18 years or older) who identified as Aboriginal or Torres Strait Islander people and attended one of ten primary health care services or service events in urban, rural and remote Australia that predominantly serve Indigenous Australians, and were able to communicate sufficiently to respond to questionnaire and interview questions. MAIN OUTCOME MEASURES:Criterion validity of the aPHQ-9, with the depression module of the Mini-International Neuropsychiatric Interview (MINI) 6.0.0 as the criterion standard. RESULTS:108 of 500 participants (22%; 95% CI, 18-25%) had a current episode of major depression according to the MINI criterion. The sensitivity of the aPHQ-9 algorithm for diagnosing a current major depressive episode was 54% (95% CI, 40-68%), its specificity was 91% (95% CI, 88-94%), with a positive predictive value of 64%. For screening for a current major depressive episode, the area under the receiver operator characteristic curve was 0.88 (95% CI, 0.85-0.92); with a cut-point of 10 points its sensitivity was 84% (95% CI, 74-91%) and its specificity 77% (95% CI, 71-83%). The aPHQ-9 was deemed acceptable by more than 80% of participants. CONCLUSIONS:Indigenous Australians found the aPHQ-9 acceptable as a screening tool for depression. Applying a cut-point of 10 points, the performance characteristics of the aPHQ were good.