We show that the non-Archimedean skeleton of the Prym variety associated to an unramified double cover of an algebraic curve is naturally isomorphic (as a principally polarized tropical abelian variety) to the tropical Prym variety of the associated tropical double cover. This confirms a conjecture by Jensen and the first author. We prove a new upper bound on the dimension of the Prym-Brill-Noether locus for generic unramified double covers of curves with fixed even gonality on the base. Our methods also give a new proof of the classical Prym-Brill-Noether Theorem for generic unramified double covers that is originally due to Welters and Bertram.Prym-Brill-Noether theory. Let X be a smooth projective curve of genus g and π : r X → X an unramified double cover. Rather than working with the components of the kernel of the norm map Nm π , it is occasionally more convenient to consider the preimage Nm −1 π (ω X ) of the canonical line bundle in Pic 2g−2 ( r X). Since the components parameterizing line bundles of positive or negative parity are naturally a torsor over Pr(X, π), the above results transfer to this setting.This point of view paves the way to studying Brill-Noether loci in Prym varieties. Fix r ě −1. In [Wel85], Welters defines the Prym-Brill-Noether locus V r (X, π) to be the closed subsetin Pic 2g−2 ( r X). Bertram's existence theorem for Prym special divisors [Ber87, Theorem 1.4] shows that this locus is non-empty, as long asfor all curves X of genus g and all unramified double covers π : r X → X. Using these two facts, Welters' Prym-Gieseker-Petri Theorem [Wel85, Theorem 1.11] implies that, for a general unramified double cover, inequality (1) is an equality.Prym-Brill-Noether theory with gonality. In contrast, very little is known about special Prym curves. Using Theorem A, and expanding on the work of Pflueger [Pfl17a] (whose use of chains of loops builds of course on [CDPR12]), we find a previously unknown upper bound on the dimension of V r (X, π) for general unramified double covers of curves X whose gonality is either even or sufficiently large.Denote by R g the moduli space of unramified double covers, as e.g. introduced in [Bea77]. We refer to the locus of unramified double covers π : r X → X for which X has gonality k ě 2 as the k-gonal locus in R g . For r ě −1, we write