Castleman's disease is a rare disorder of the lymphoid tissue with three possible histological variants--the hyalin-vascular type, with a good prognosis, the plasma-cellular type and the mixed type; the latter two are both more aggressive than the hyalin-vascular type. Two clinical types of this disease have already been described: the localized or unifocal type and the multicentric or multifocal type. The aetiology of Castleman's disease remains unclear due to polymorphic clinical features that give rise to many diagnostic and treatment problems. Its diagnosis, therefore, can only be confirmed by histological examination. Surgical treatment is the treatment of choice in patients with Castleman's disease, but radical removal of the tumour mass, especially in the multicentric type, is not always possible. We are still in no position to draw definitive conclusions as to treatment, because there are only a few reports with different regimens regarding patients with multicentric Castleman's disease. A better understanding of the pathogenesis of this rare disorder may help in deciding the best treatment approach. In this study, we report two cases of Castleman's disease, one hyalin-vascular and the other plasma-cellular, both of which were unifocal and located in a retroperitoneal-pararenal site. We also analyse the main clinical, diagnostic and treatment problems associated with this rare condition, with an overview of the literature.