Retroperitoneal space abscesses are a life-threatening illness which is difficult to diagnose and treat because of both their rarity and insidious clinical manifestations. The insidious development of this illness is a challenge for all medical and surgical subspecialists. The discovery of the real source of the infection is very important but not always possible, and knowledge of the anatomy and borders of the retroperitoneal space is helpful in understanding all such atypical cases and for establishing a definitive treatment. Two cases are reported that are both characterized by rare causes, uncommon development, and atypical manifestation. The normally undefined inferior borders of some parts of the retroperitoneal space or previous retroperitoneal surgery could have been the cause of the abnormal and misleading development of the abscesses. Chronically infected organs can be the true origin of this abscess, and their discovery in a nonemergency situation is mandatory for complete surgical treatment. These cases show that knowledge of the anatomy of the retroperitoneal space is important to establish the suspicion of an abscess, to understand its manifestations, which are sometimes caused by a rare pathophysiology, and to initiate appropriate treatment.