Angiogenic factor with G-patch and FHA domain 1 (AGGF1) is a novel angiogenic factor that was first described in Klippel-Trenaunay syndrome, a congenital vascular disease associated with capillary and venous malformations. AGGF1, similar to vascular endothelial growth factor (VEGF), has been shown to promote strong angiogenesis in chick embryos in vivo. Blocking AGGF1 expression prevented vessel formation, which suggests AGGF1 is a potent angiogenic factor linked to vascular malformations. So far, AGGF1 expression studies in human vascular lesions have not been performed. Here, we immunohistochemically investigated AGGF1 expression in venous, arteriovenous or capillary malformations, and infantile or congenital hemangioma. We found that AGGF1 was mostly expressed in endothelial cells with plump morphology. Moreover, the majority of mast cells strongly expressed AGGF1. Notwithstanding our incomplete knowledge of the molecular mechanism of AGGF1 in angiogenesis, our results show for the first time that AGGF1 is expressed in plump endothelial cells and mast cells.