This study investigated the perception of discrepancies between the dental and facial midlines by orthodontists and young laypeople. A smiling photograph of a young adult female was modified by moving the dental midline relative to the facial midline. Twenty orthodontists (10 males and 10 females) and 20 young adult laypeople (10 males and 10 females) scored the attractiveness of the smile on the original image and each of the modified images using a 10-point scale. The results showed that the images were scored as less attractive both by the orthodontists and laypeople as the size of the dental to facial midline discrepancy increased. The scores were unrelated to the direction of the midline discrepancy (left or right) or to the gender of the judge. Further analysis revealed that the orthodontists were more sensitive than laypeople to small discrepancies between the dental and facial midline. It was estimated that the probability of a layperson recording a less favourable attractiveness score when there was a 2-mm discrepancy between the dental and facial midlines was 56 per cent.