This dissertation contains a critical edition of the early Irish tale Aided Derbforgaill “the violent death of Derbforgaill”. It includes an introduction discussing the main thematic components of the tale as well as intertextuality, transmission and manuscript relationship. The edition is accompanied by transcripts from the three manuscript copies of the tale and textual notes. Aided Derbforgaill is an Ulster Cycle tale and belongs to a category of tales describing the death of prominent heroes, rarely heroines, in early Irish literature. Arriving in the shape of a bird to mate with the greatest of all heroes, Cú Chulainn, Derbforgaill is refused by Cú Chulainn on account of him having sucked her blood. Forced to enter a urination competition between women, and upon winning this, Derbforgaill is mutilated by the other competitors. The tale ends with two poems lamenting the death of Derbforgaill. This very short tale is complex, not only in its subject matter, but in the elliptical language of the poetry. Thematically the tale is a combination of very common motifs found elsewhere in early Irish literature, such as the Otherworld, metamorphosis and the love of someone unseen, and some rare motifs that are almost unique to this tale, such as blood sucking and the urination competition. The text also have clear sexual overtones.