Three hundreds percutaneous renal biopsy cases were analyzed for recorded clinical complications retrospectively. Incidence of fever (> or = 37.5 degrees C), pain, and decrease in hematocrit (> or = 4%) was 21%, 28%, and 13% respectively. The incidence of fever and pain were less in the older patients. Prospectively, 125 cases who underwent ultrasonography following renal biopsies and 62 cases who underwent computerized tomography were analyzed. Bigger hematoma was followed by fever 5-7 days after renal biopsies. Incidence of pain and the decrease in hematocrit were correlated with the size of hematoma. Use of the ultrasonographic localization and a Tru-Cut biopsy needle or a Biopty-Cut needle decreased the incidence of hematoma more than 50ml following renal biopsy (0-5%). Incidence of fever and pain was less by these new procedure. The risk of hematoma increased as the biopsy needle went deeper into medulla.