The final stage in the medical imaging diagnostic system is the radiologist’s interpretation of the images, though research on the factors influencing performance in digital breast tomosynthesis (DBT) is inconclusive. This study seeks to understand the performance of radiologists in reading DBT images and the parameters impacting observer performance in three different countries. The study used a DBT mammogram test to compare the performance of radiologists from Australia, China and Iran in reading thirty-five DBT cases. A range of performance metrics including specificity, sensitivity, lesion sensitivity, ROC AUC and JAFROC FOM were generated for each radiologist upon the conclusion of the test set. The radiologists also provided demographic information relating to their experience in reading digital mammograms and DBT. Each country had a greater percentage of radiologists that have completed a breast imaging fellowship compared to those that have not. Australia had a greater percentage of radiologists that have completed training in DBT reading (Australia=88.2%), while China and Iran had a smaller percentage of radiologists that have not completed training in DBT reading (China=37%, Iran=40%). Significant differences were identified between the three countries in specificity (p=.001), lesion sensitivity (p=.016), ROC (p<.001) and JAFROC (p<.001). Australia had the highest mean value for all performance metrics, while China had the lowest mean value for all performance metrics. Australian radiologists have a moderate positive correlation between lesion sensitivity and the number of years reading DBT images (r=.513, p=.042). Iranian radiologists who read more than 20 DBT cases per week obtained significantly higher performance in lesion sensitivity 73.3% vs. 51.8%; p=.032) than the ones who read less than 20 DBT cases per week.