The high prevalence of co-occurring mental health and substance use disorders in young people is well established. Despite this, there are low rates of detection of co-occurring disorders across alcohol and other drug (AOD) services within Australia. This paper describes the development, implementation and evaluation of a mental health screening tool and training programme within the youth AOD sector. Thirty youth AOD workers received training in mental health screening, and the screening tool was subsequently piloted on 84 young people accessing two youth AOD services. Training was evaluated using measures of the trainee's mental health knowledge, attitudes, skills and confidence in mental health screening at baseline and 12-month follow-up. Feedback from young people supported the feasibility, acceptability and relevance of the screening tool. Evaluation of the associated training programme indicated improvements in AOD workers' mental health knowledge, skills and confidence in mental health screening. These findings provide preliminary evidence of the feasibility and acceptability of the mental health screening tool to young people and the effectiveness of the training package within the youth AOD sector.