Among renal abnormalities the hypo-plastic kidney is one of the least well defined, both nosographically, due to lack of any precise morphological definition and, terminologically, because of wide gaps in aetio-pathogenetic knowledge. From hundreds of bizarrely-shaped and odd-looking kidneys, diminutive in size, some seem to be isolated from the rest and show a set of common anatomical features suggesting that they belong more or less to the same family, possibly as a result of similar embryological defects. Their minor calices are both less numerous and less developed than is normal, so that the pyramids, lobes and successive generations of nephrons that have grown from them are consequently scarce and underdeveloped. Whether or not these abnormal kidneys can be systematically ranged under one unique family name is the most important question. Secondly, until we get the right word from histology or embryology, should the term hypoplastic be kept for this group?.