Four cases of congenital renal malformations in monkeys are reported. They consisted of fusion and ectopy of the kidneys in a squirrel monkey (Saimiri sclurea), a polycystic kidney in a pigtail macaque (Macaca nemestrina), cortical cystic kidneys in a squirrel monkey (Saimiri sciurea) and unilateral partial renal aplasia in a howler monkey (Alouatta caraya).