A series of studies was conducted to adapt the Australian Self-reported Delinquency Scale (Mak, 1993) for use with adolescents in the State of Western Australia. First, an item construction and analysis study was conducted to determine whether variations in State laws and rules between the Australian Capital Territory (where Mak's scale was developed) and Western Australia would require the deletion or addition of items to the present scale. As a result of this study, two items were deleted and six items were added to the scale. Second, the factor structure and content validity of the scale were tested by examining the item responses of 230 high-school students to determine whether the same nine factors obtained by Mak would be yielded. The outcomes of this analysis identified seven factors, which were labelled theft and burglary, motor vehicle offences, drug-related offences, assault, vandalism, public disorder, and school-related offences. Finally, the scale was validated by comparing the item responses of 260 adolescents (80 delinquent, 90 at-risk, and 90 not at-risk adolescents) with the item responses of the Phase 2 sample using MICFA and the coefficient of congruence procedure. In line with Mak's findings, the outcomes of this study have shown the instrument to be highly reliable, indicating that the factors are dependable across different data sets, and that the values are sufficiently high to investigate meaningful group differences.