Renal hypoplasia is a developmental anomaly in which one or both kidneys (unilateral or bilateral renal hypoplasia, respectively) have a deficit in the number of nephrons and may be small. Oligomeganephronia represents a severe variant of hypoplasia in which nephron number is reduced by 80% and nephrons are markedly hypertrophied. The disease is renal hypoplasia (MONDO_0019637). Also known as: renal hypoplasia (disease).