Retroperitoneal fibrosis is an uncommon inflammatory disease that leads to extensive fibrosis throughout the retroperitoneum. The majority of cases are idiopathic. The characteristic perivascular distribution of the idiopathic form supports the theory that the disease is an immune-mediated response to severe atherosclerosis. Evidence suggests that idiopathic retroperitoneal fibrosis may be part of a systemic fibrosing disease. Other less common forms include methysergide-related and malignant retroperitoneal fibrosis. The signs and symptoms of the disease are vague and nonspecific, and therefore the diagnosis relies heavily on radiologic findings. Once the diagnosis is suggested, the distinction must be made between malignant and nonmalignant retroperitoneal fibrosis, because the prognosis is dismal for malignant retroperitoneal fibrosis, but very good for other forms of the disease. Surgical biopsy remains the only way to definitively establish this diagnosis. Treatment may be surgical or medical, with the best outcome observed in patients receiving both.