OBJECTIVE. Persistent concern exists about the variable and possibly inappropriate utilization of high-cost imaging tests. The purpose of this study is to assess the influence of appropriate use criteria attributes on altering ambulatory imaging orders deemed inappropriate. MATERIALS AND METHODS. This secondary analysis included Medicare Imaging Demonstration data collected from three health care systems in 2011-2013 via the use of clinical decision support (CDS) during ambulatory imaging order entry. The CDS system captured whether orders were inappropriate per the appropriate use criteria of professional societies and provided advice during the intervention period. For orders deemed inappropriate, we assessed the impact of the availability of alternative test recommendations, conflicts with local best practices, and the strength of evidence for appropriate use criteria on the primary outcome of cancellation or modification of inappropriate orders. Expert review determined conflicts with local best practices for 250 recommendations for abdominal and thoracic CT orders. Strength of evidence was assessed for the 15 most commonly triggered recommendations that were deemed inappropriate. A chi-square test was used for univariate analysis. RESULTS. A total of 1691 of 63,222 imaging test orders (2.7%) were deemed inappropriate during the intervention period; this amount decreased from 364 of 11,675 test orders (3.1%) in the baseline period (p < 0.00001). Of 270 inappropriate recommendations with alternative test recommendations, 28 (10.4%) were modified, compared with four of 1024 inappropriate recommendations without alternatives (0.4%) (p < 0.0001). Seventy-eight of 250 recommendations (31%) conflicted with local best practices, but only six of 69 inappropriate recommendations (9%) conflicted (p < 0.001). No inappropriate recommendations that conflicted with local best practices were modified. All 15 commonly triggered recommendations had an Oxford Centre for Evidence-Based Medicine level of evidence of 5 (i.e., expert opinion). CONCLUSION. Orders for imaging tests that were deemed inappropriate were modified infrequently, more often with alternative recommendations present and only for appropriate use criteria consistent with local best practices.