Background: Attitude to, and confidence in, working with comorbidity is an important feature of effective engagement when working with clients with mental health and substance use issues. Substance use treatment clinicians continue to voice concerns about their own skill and abilities to work with this complex client group. PsyCheck is a package designed to support drug and alcohol workers to implement screening and brief intervention for common mental health problems. Aim: This study used a whole workforce approach to training using the PsyCheck package, and examined changes in clinicians' attitude, skill and confidence in working with comorbidity post training. Method: A pre-post test evaluation design was used. Thirteen national alcohol and drug services were offered a two day training program in the PsyCheck package. Clinicians' attitude to Comorbidity was measured by the Comorbidity Problems Perceptions Questionnaire. Semi-structured interviews were also conducted. Results: Results indicate that involvement in the training program was, overall, a positive experience for clinicians. Attitude to, and confidence in, working with comorbidity appeared to improve following exposure to the training. Conclusions: Although there are limitations in the design, training appears to have a positive impact on clinicians self reported attitudes and confidence in dealing with comorbidity issues. �� 2010 Taylor & Francis.