Renal agenesis (RA) is a form of renal tract malformation characterized by the complete absence of development of one or both kidneys (unilateral RA or bilateral RA respectively), accompanied by absent ureter(s). The disease is renal agenesis (MONDO_0018470, a Monarch Disease Ontology entry). Also known as: absent/small kidney, absent/underdeveloped kidney, hereditary renal aplasia, hereditary urogenital adysplasia, renal adysplasia, renal agenesis (disease), renal agenesis/hypoplasia, renal aplasia.