Most patients with renal infarction give a history of having had one or more prevoius attacks of myocardial infarction. Pain, the most common symptom, is sudden in onset, unilateral, severe, unremitting, and prostrating. The infarct may be arterial (caused by embolism or thrombosis), venous (hemorrhagic, with or without thrombosis of the renal vein), or traumatic. The importance of differential diagnosis is illustrated in the seven case histories here given, since the two patients with arterial infarcts recovered on conservative management while those with other types of renal lesions had to be treated surgically. Arterial infarction of a kidney is fairly common and should be diagnosed accurately. If it is unilateral, it seldom needs surgical treatment.