The forkhead box f1 (Foxf1) transcription factor is expressed in the visceral (splanchnic) mesoderm, which is involved in mesenchymal-epithelial signaling required for development of organs derived from foregut endoderm such as lung, liver, gall bladder, and pancreas. Our previous studies demonstrated that haploinsufficiency of the Foxf1 gene caused pulmonary abnormalities with perinatal lethality from lung hemorrhage in a subset of Foxf1+/- newborn mice. During mouse embryonic development, the liver and biliary primordium emerges from the foregut endoderm, invades the septum transversum mesenchyme, and receives inductive signaling originating from both the septum transversum and cardiac mesenchyme. In this study, we show that Foxf1 is expressed in embryonic septum transversum and gall bladder mesenchyme. Foxf1+/- gall bladders were significantly smaller and had severe structural abnormalities characterized by a deficient external smooth muscle cell layer, reduction in mesenchymal cell number, and in some cases, lack of a discernible biliary epithelial cell layer. This Foxf1+/- phenotype correlates with decreased expression of vascular cell adhesion molecule-1 (VCAM-1), alpha(5) integrin, platelet-derived growth factor receptor alpha (PDGFRalpha) and hepatocyte growth factor (HGF) genes, all of which are critical for cell adhesion, migration, and mesenchymal cell differentiation.