Transrectal ultrasonography has proved valuable in assessing the effect of primary treatment modalities for prostate carcinoma. This study shows patients who had a significant reduction in primary tumor volume had a significantly better prognosis and had less local symptoms than did the group of patients that did not have a significant reduction (less than 50%) in primary volume secondary to therapy. Patients were treated with either castration or Zoladex and all had Stage D2 cancer of the prostate.