SUMMARYChronic medullary necrosis is a variant of chronic pyelonephritis. Many cases are associated with phenacetin abuse and some with diabetes. Obstruction is uncommon.It is seen mainly in middle‐aged females.The lesion is an ischaeniic infarct and as this distinctive, with formation of a ring shadow and later a cavity.Most papillae of both kidneys ar usually involved. Concretions are frequent.Most kidneys shrink and dye excretion 0n intravenous urography is diminished, both due to pyelonephritis.The clinical features are mainly those of urinary tract infection and tend to parallel the urographic findings.The disease tends to have a cyclic course with remissions but usually deterioration occurs.Treatment is directed to any predisposing factors and to eliminating infectio