The origin of hybrid individuals is often difficult to diagnose from phenotypic characters, and many hybrids may go unrecognized because they are morphologically ambiguous or similar to one of the parental species. We describe an unusually well-characterized intergeneric hybridization event in the Parulidae, and use it to validate DNA-based diagnosis of the parental species. Three hybrid wood-warbler fledglings resulting from a cross between a male Black-and-white Warbler (Mniotilta varia) and a female Yellow-rumped Warbler (Dendroica coronata) were discovered in 2000 in the Montréal Biodôme free-flight aviary. This is the first time these two species have been known to hybridize. Two individuals died as fledglings, whereas one remains alive in the Biodôme at present, providing an unusual opportunity to describe the plumage phenotype of a hybrid wood-warbler across age classes and the complete annual molt cycle. Diagnosis of this hybrid would have been difficult using traditional methods, as its plumage appears to be a slightly aberrant Mniotilta, whereas it is intermediate between the parental species in mensural and song characters. We compared the sequences of both mitochondrial DNA and nuclear-encoded intron loci to a comprehensive data base from nearly all Parulidae and confirmed the hybrid's parental species.