As mental health providers increasingly adopt evidence-based practices, tools are needed to assess practitioner knowledge of these practices. We describe the development and psychometric evaluation of a paper-and-pencil test to assess provider attitudes and knowledge about Integrated Dual Disorders Treatment (IDDT). In this sample of clinicians who were implementing IDDT in two mental health centers, the test showed good internal consistency, inter-rater reliability, and for a subsample who took the test twice, significant improvement over time. Higher scores on the scale were correlated with greater education, but not greater experience or lower burnout. This test is a promising tool for assessing provider knowledge of a specific evidence-based practice.