Becker, Blasius, Rhodius, Baillie, Portal, Sandifort, Meckel, Schenck, and Stoll are among the older writers who have observed the absence of one kidney.

In a recent paper Ballowitz has collected 213 cases, from which the following extract has been made by the British Medical Journal:-- "Ballowitz (Virchow's Archiv, August 5, 1895) has collected as far as possible all the recorded cases of congenital absence of one kidney.
Excluding cases of fused kidney and of partial atrophy of one kidney, he finds 213 cases of complete absence of one kidney, upon which he bases the following conclusions: Such deficiency occurs almost twice as often in males as in females, a fact, however, which may be partly accounted for by the greater frequency of necropsies on males.

As to age, 23 occurred in the fetus or newly born, most having some other congenital deformity, especially imperforate anus; the rest were about evenly distributed up to seventy years of age, after which only seven cases occurred.

Taking all cases together, the deficiency is more common on the left than on the right side; but while in males the left kidney is far more commonly absent than the right, in females the two sides show the defect equally.

The renal vessels were generally absent, as also the ureter, on the abnormal side (the latter in all except 15 cases); the suprarenal was missing in 31 cases.