For many applications measuring the similarity between documents is essential. However, little is known about how users perceive similarity between documents. This paper presents the first large-scale empirical study that investigates perception of narrative similarity using crowdsourcing. As a dataset we use a large collection of Dutch folk narratives. We study the perception of narrative similarity by both experts and non-experts by analyzing their similarity ratings and motivations for these ratings. While experts focus mostly on the plot, characters and themes of narratives, non-experts also pay attention to dimensions such as genre and style. Our results show that a more nuanced view is needed of narrative similarity than captured by story types, a concept used by scholars to group similar folk narratives. We also evaluate to what extent unsupervised and supervised models correspond with how humans perceive narrative similarity.