This article explores the relationship between existentialism and the horror genre. Noël Carroll and others have proposed that horror monsters defy established categories. Carroll also argues that the emotion they provoke - 'art-horror' - is a 'composite' of fear and disgust. I argue that the sometimes horrifying images and metaphors of Sartre's early philosophy, which correlate with nausea and anxiety, have a non-coincidental commonality with art-horror explained by existentialism's preoccupation with the interstitial nature of the self. Further, it is argued that, as with some of the more sophisticated examples of the horror genre, the way for existential protagonists like Roquentin and Gregor Samsa to meet the challenge of the horrifying involves an accommodation of these features of the existential condition within their developing identity, which results in them appearing monstrous to others. Lastly, it is claimed that the association between existentialism and art-horror can explain the (paradoxical) appeal of horror.