['Retroactive interference occurs when newly acquired information inhibits recall of previously learned information. This has been shown to influence recall of sounds, tastes and word associations, and is typically seen when learners receive training on one area of content and are then exposed to new content before being evaluated on the original content. Thus far, retroactive interference has received little attention in medical education and has not been studied during simulation training. Our objective was to evaluate whether retroactive interference occurs during simulation training.', 'We randomised 167 Year 1 medical students to one of two training protocols. After training on a cardiac murmur, participants were tested either on the same cardiac murmur followed by a novel murmur (the non-interference protocol), or on the novel murmur followed by the training murmur (the interference protocol). We evaluated performance on both murmurs at 1 hour and 6 weeks post-training.', 'We found a significant interaction between training protocol and diagnostic performance on training versus novel murmurs at both testing time-points. Students in the non-interference protocol had increased odds of achieving success on the training murmur relative to the novel murmur at 1 hour (odds ratio [OR] 4.96; p < 0.001) and at 6 weeks (OR 4.23; p = 0.001) after training. By comparison, students in the interference protocol did not demonstrate improved performance on the training murmur relative to the novel murmur at either evaluation (1 hour post-training: OR 0.56 [p = 0.08]; 6 weeks post-training: OR 0.66 [p = 0.23]).'] Is learning during simulation training prone to retroactive interference?