The specification and morphogenesis of an organ requires the coordinate deployment and integration of regulatory information, including sex specific information when the organ is sex specific. Only a few gene networks controlling size and pattern development have been deciphered, which limits the emergence of principles, general or not, underlying the organ-specifying gene networks. Here we elucidate the genetic and molecular network determining the control of size in the Drosophila abdominal A9 primordium, contributing to the female genitalia. This network requires axial regulatory information provided by the Hox protein Abdominal-BR (Abd-BR), the Hox cofactors Extradenticle (Exd) and Homothorax (Hth), and the sex specific transcription factor Doublesex Female (DsxF). These factors synergize to control size in the female A9 by the coordinate regulation of the Decapentaplegic (Dpp) growth pathway. Molecular dissection of the dpp regulatory region and in vivo protein interaction experiments suggest that Abd-BR, Exd, Hth and DsxF coordinately regulate a short dpp enhancer to repress dpp expression and restrict female A9 size. The same regulators can also suppress dpp expression in the A8, but this requires the absence of the Abd-BM isoform, which specifies A8. These results delineate the network controlling female A9 growth in Drosophila.