Castleman's disease is a localized, rare and benign hyperplasia of the lymph nodes, occurring mainly in the mediastinum. Three histologic types--hyalinvascular, plasmacellular and intermediate--have been recognized. We report on two patients with unusual locations of the disease, i.e. the pelvis and the retroperitoneum respectively. These observations show that diagnosis is difficult. They also indicate that, in selected patients, radiotherapy may induce tumor regression and allow the resection of apparently inoperable lesions