Aim This study aimed to compare the predictive value of D-dimer and a clinical prediction score in diagnosis of pulmonary embolism (PE) as this could improve practice and reduce costs simultaneously. Method To achieve this, medical records of patients who presented to the Emergency Department of a large Australian metropolitan general hospital over 12 months and underwent DD testing were reviewed. The correlation coefficient (CC) was calculated using the Cramer’s V method. Results CC between low-, intermediate- and high-risk groups on their own and a final diagnosis of PE on imaging was 0.1332, 0.1278 and 0.0817, respectively. By contrast, the CC when using positive DD was higher for all categories: 0.7527, 0.6256 and 0.4195, respectively. For the age-adjusted DD, the correlations were higher than for the clinical prediction score but less than for the absolute DD; calculated at 0.6490, 0.4987 and 0.3550 for the respective groups. The overall CC for risk category was 0.1107; for a positive DD, it was 0.7033; for the age-adjusted DD, it was 0.5928. Conclusion Positive DD has a higher correlation with PE diagnosis than the clinical prediction score. DD assay, whether positive or negative, is therefore an invaluable test in assessment of patients with suspected PE and can help determine the need for tomographic imaging. The absolute DD is more useful than the age-adjusted value.