In Xenopus and zebrafish embryos, elongation of the anterior-posterior body axis depends on convergent extension, a process that involves polarized cell movements and is regulated by non-canonical Wnt signaling. The mechanisms that control axis elongation of the mouse embryo are much less well understood. Here, we characterize the ENU-induced mouse mutation chato, which causes arrest at midgestation and defects characteristic of convergent extension mutants, including a shortened body axis, mediolaterally extended somites and an open neural tube. The chato mutation disrupts Zfp568, a Krüppel-associated box (KRAB)domain zinc-finger protein. Morphometric analysis revealed that the definitive endoderm of mouse wild-type embryos undergoes cell rearrangements that lead to convergent extension during early somite stages, and that these cell rearrangements fail in chato embryos. Although non-canonical Wnt signaling is important for convergent extension in the mouse notochord and neural plate, the results indicate that chato regulates body axis elongation in all embryonic tissues through a process independent of non-canonical Wnt signaling.