Six hundred thirty-two percutaneous renal biopsies were performed in 479 patients between 1965 and 1978. Complications occurred with 86 biopsies, an incidence of 8.5 per cent. Most complications (seventy-six of eighty-six) were minor, and either resolved spontaneously or did not require intervention. There were ten major complications, including 6 patients with gross hematuria requiring blood transfusions, 3 with hemorrhage treated with arterial embolization, and 1 with a symptomatic arteriovenous fistula that was treated with partial nephrectomy. Major complications of percutaneous renal biopsy and the modes of therapy are discussed.