BACKGROUND: Fibroblast Growth Factor 9 (Fgf9) and its paralog Fgf20 are expressed in the developing stomach. We investigate the role of these growth factors during gastric development, using combinations of null alleles. RESULTS: Analysis of expression databases showed that Fgf9 is expressed in gastric endoderm and surrounding mesoderm such as the mesothelium as early as E8.5, and Fgf20 is expressed in the gastric progenitors of the glandular stomach. To explore whether Fgf9 and Fgf20 are important for gastric development, we examined embryonic stomachs from Fgf9 and Fgf20 null (Fgf9 CONCLUSIONS: Fgf9 drives gastric growth and squamous epithelial identity during gastric development.