Purpose:To evaluate the feasibility of irradiat ion to the metastatic retroperitoneal lymph nodes using three-dimensional confo rmal radiotherapy (3-DCRT) and to assess the irradiation side effects. Methods:From Jun. 1997 to Sep. 2000, 52 patients of metastatic retroperitoneal lymph nodes were treated with 3-DCRT.These patients had receive d radical therapy for their primary tumors. 50 of them had been proved by pathol ogical examination. Radiotherapy was designed by Elekta company’s 3-D treatmen t plan. Dose volume histography (DVH) was used to verify and optimize the radiat ion plan. Using 5～6 conformal portals,the total irradiation dose was 40 Gy an d delivered at 4～5Gy per fraction every other day,to a total of 8～10 fractions in 16～20 days. The immediate responses and side effects were evaluated accordi ng to the WHO and RTOG criterion system. Results:According to Karnofsky criterion system the median scor e was raised 21.3. Three months after irradiation, the complete ,partial and tot al response rates were 38.6%(27/70), 54.3%(38/70)and 92.9%(65/70),respect ively. The early response was related to the target volume and pathological clas sification. The smaller the target volume, the better the response(? 2 = 1 5.211,P=0.004).The anaplastic carcinoma cases had better results than the squamous carcinomas and adenocarcinomas(? 2 =13.455,P=0.009).The 1- ,2- and 3- year survival rates were 59.6%(31/52)、23.1%(12/52)and 9.6%(5/ 52),respectively. Conclusions:Three dimensional conformal radiotherapy can be con sidered as an effective and feasible approach for the treatment of metastatic r etroperitoneal lymph nodes,and no serious complications were observed.