Mutations in the ken and barbie locus are accompanied by the malformation of terminalia in adult Drosophila. Male and female genitalia often remain inside the body, and the same portions of genitalia and analia are missing in a fraction of homozygous flies. Rotated and/or duplicated terminalia are also observed. Terminalia phenotypes are enhanced by mutations in the gap gene tailless, the homeobox gene caudal, and the decapentaplegic gene that encodes a TGFβ‐like morphogen. The ken and barbie gene encodes a protein with three CCHH‐type zinc finger motifs that are conserved in several transcription factors such as Krüppel and BCL‐6. All defects in ken and barbie mutants are fully rescued by the expression of a wild‐type genomic construct, which establishes the causality between phenotypes and the gene. Arch. Insect Biochem. Physiol. 54:77–94, 2003. © 2003 Wiley‐Liss, Inc.