None of the non surgical methods for investigations of the lymph node extension of prostate carcinoma is entirely satisfactory. However, the risk of lymphatic extension is correctly appreciated when the initial tumor is well documented by rectal examination and endo-rectal ultrasonography. Histology shows an increasing interest. IVP, CT scan are of little interest for micrometastases while the results of lymphography are improved by cytoaspiration of abnormal models. Lymphadenectomy gives the most accurate appreciation of the lymphatic extension. The reliability of frozen sections interpretation is now very satisfactory. When limited to the triangle: external iliac artery, internal iliac artery and obturator fossa, the morbidity is reduced. In case of negative lymph nodes, radical prostatectomy gives to the patients a reasonable chance of complete cure.