Congenital tumors are rare in cattle. In this case report, a calf with a congenital perirenal fibrosarcoma is described. A newborn Belgian Blue calf that succumbed shortly after caesarian section was submitted for necropsy at the diagnostic lab of the ARSIA (Association Régionale de Santé et d’Identification Animales). At necropsy, a hemorrhagic firm mass was found surrounding the left kidney. Histopathological examination of the mass revealed a neoplastic cell population. Additional immunohistochemical stainings were performed to identify the tumor. The majority of neoplastic cells stained positive for vimentin but were negative for neurofilaments (NFs), desmin, CD3, CD20, Von Willebrand factor and cytokeratin, indicating a mesenchymal origin. The tumor was diagnosed as a fibrosarcoma. To the authors’ knowledge, this is the first case of a congenital perirenal fibrosarcoma reported in a Belgian Blue calf in Belgium.