Marked regression with areas of necrosis and hemorrhage as well as cysts is not uncommon in hypernephromas and has been described by GRAWITZ (1883), ISRAEL (1925) and LJUNGGREN (1930). Both LJUNGGREN and ISRAEL pointed out that in certain cases it may be extremely difficult at operation to distinguish between a solitary renal cyst and a hypernephroma that has undergone cystic transformation. There are cases recorded (ALBRECHT 1905, FABRICIUS 1911, ARKIN 1926, MORO 1933, GOLDSTEIN & ABESHOUSE 1938) in which the regressive changes were so conspicuous that the primary tumor appeared to have healed but in several of these cases recurrences or metastases subsequently developed. Spontaneous healing of hypernephromas may nevertheless occur, as first reported by HULTQUIST (1944). In 1950 BARTLEY & HULTQUIST collected 26 cases of spontaneously healed hypernephromas. All the growths were incidental findings at autopsy and ranged in size from a bean to a cherry; they were usually encapsuled and had characteristic macroscopic and microscopic appearances. Some of the tumors contained cysts but the morphology was basically uniform. The series was subdivided into three groups as regards the presence of tumor cells. The tumors in group III had distinct but relatively sparse hypernephroma cells. In group II a few hypernephroma-like cells with marked regressive changes were manifest, while in group I no tumor cells were present.