The vestigial (vg) locus of Drosophila melanogaster is involved in wing margin development. In the absence of a vg+ gene, extensive cell death occurs in third instar imaginal discs which results in a complete loss of adult wing margin structures. P-element tagging was used to obtain a molecular clone of the vg locus, which led to the molecular characterization of approximately 46 kb of DNA from the region. Deficiency analysis and molecular mapping identified sequences, spanning approximately 20 kb of DNA within the larger region, which are necessary for vg function. The molecular map was oriented with respect to a pre-existing genetic fine structure map of the locus. The centromere distal limits of the locus were defined by deficiency analyses while the proximal end has not yet been conclusively established. However, three transcripts, that are apparently unrelated to vg, provide circumstantial evidence for the proximal limits of the vg locus. The nature of the molecular lesions for several extant recessive or lethal vg alleles was determined, and these were placed on the vg molecular map. The characterization of the lesions associated with two dominant vg alleles and one complex vg allele imply interesting regulatory mechanisms for this locus. As well, a revertant of a 412 insertion mutant allele was shown to have resulted from a further insertion of a roo element into the 412 element.