BackgroundPrenatal alcohol exposure (PAE) can result in permanent disability, including physical, neurodevelopmental, and cognitive impairments, known as fetal alcohol spectrum disorder (FASD). Individuals with FASD are more likely to engage with the law, including being placed in detention, than individuals without FASD. Young people who were sentenced to detention participated in a FASD prevalence study in Western Australia. The diagnosis of FASD requires a multidisciplinary assessment and confirmation of maternal alcohol consumption during pregnancy. Obtaining accurate assessment of PAE for young people participating in the study was challenging.MethodsAn interview with the birth mother or other responsible adult for young people sentenced to detention in Western Australia was conducted as part of the FASD assessment. The Alcohol Use Disorders Identification Test consumption subset (AUDIT‐C), other relevant questions, and documentary evidence were used to assess PAE. PAE was categorized according to the Australian Guide to the Diagnosis of FASD: no PAE reported, confirmed or confirmed high‐risk, or unknown.ResultsAmong the 101 participants, information on PAE was unable to be obtained for 13 (13%) young people. Of the remaining 88 participants with information of PAE, 41 reported no PAE and 47 had confirmed PAE.ConclusionsAccurately assessing prenatal alcohol consumption is challenging in any setting, but it is exceptionally challenging when assessed 13 to 17 years retrospectively as part of a FASD assessment for a young person sentenced to detention. Recording and recoding detailed qualitative responses was required to provide an accurate assessment of PAE using the AUDIT‐C. Standardized recording of PAE in antenatal and birth records would facilitate later assessments for FASD and provide opportunities for advice and support for women who continue to drink during pregnancy.