Objective: To evaluate what specific combination of clinical criteria and d-dimer values may yield at least a 10% positive pulmonary embolism (PE) rate in patients undergoing pulmonary CT angiography (CTA). Materials and Methods: Retrospective review of all patients presenting to the Emergency Department with possible PE who underwent pulmonary CTA and had a d-dimer drawn. Wells scores were retrospectively assigned based on data gathered through medical records. Results: During a 29-month period, 1110 patients underwent pulmonary CTA. Of these, 773 also had a d-dimer drawn. These subjects were stratified based on serum d-dimer levels into negative (≤4 μg/ml), nonpositive (0.41 - 1.0 μg/ml), or positive (>1.0 μg/ml) d-dimer categories. The prevalence of positive CTA studies was >10% only in the positive d-dimer group. Subjects were also stratified based on their Wells score into three clinical categories: low (score < 2), intermediate (score = 2 - 6), and high risk of pulmonary embolism (score > 6). The prevalence of positive CTA was > 10% only in the group of subjects with high clinical risk. When stratified according to both Wells criteria and d-dimer, only those patients with intermediate or high clinical risk combined with a positive d-dimer (>1.0 μg/ml) had a prevalence of positive pulmonary CTA > 10%. By limiting the use of CTA studies to those patients with positive d-dimer values or high clinical risk, 438 (55.4%) patients could have avoided CTA imaging. Conclusion: Utilizing CTA only in patients suspected of PE with a combination of high clinical risk based on a Wells criteria threshold score > 6 and a serum d-dimer cutoff of 1 μg/ml would increase the prevalence of positive pulmonary CTA studies above 10% and avoid a large number of CTA imaging studies.