Taking into consideration anthropological theories of liminality, the episode of the “sierra y de los amores con las serranas” in the Libro de buen amor acquires a new dimension that is suitable to negotiate gender and sexual behavior. The sierra, as well as its inhabitants, is presented in a manner that situates it far away, geographically and temporally, from the Archpriest’s society. It can be considered part of a “liminal” universe where notions of gender identity are transformed and masculine and feminine behavior is reversed. However, these reversals are not long lasting and they are contained within a specific frame, similar to that of ritual. Due to the liminal frame that surrounds this episode, the negotiations of gender do not represent a threat to the hegemony of urban society. Nonetheless, the mere representation of an alternative female model, even if it is a negative and liminal one, points to the impossibility of setting permanent gender roles in a society and a book that is in constant transition and negotiation.