Fourty nine patients having a prostatic carcinoma had a CT examination. CT should be used only if bone metastasis lack and if a curative treatment is possible. Study of local extension is misleading and ultrasound, especially transrectal, is a better method to appreciate the volume of the tumor. On the contrary, CT detects quite often nodes metastasis which will modify the treatment. If CT is negative, lymphangiogram must be done because it is a more precise method to evaluate the node structure. Percutaneous node biopsy may confirm node metastasis.