Idiopathic retroperitoneal fibrosis was first reported in 1948. Its etiology is unknown. It is not primarily a urological condition although it usually manifests itself by urological symptoms. The fibrotic process seems to originate about the great vessels and to spread from them, enveloping, but not usually invading, the retroperitoneal structures. Among these the ureter is the most vulnerable, and its obstruction inevitably results in damage to the kidney. The two cases here described, and analysis of succeeding case reports show that such fibrosis is sometimes responsible for obscure but severe abdominal and back pains. It was unrecognized and proved fatal in a 45-year-old man; in the second patient, a 43-year-old man, exploratory laparotomy led to the diagnosis, and liberation of the ureters from the surrounding fibrotic structures restored the patient to health.