Ninety-five percutaneous renal biopsies under ultrasound guidance were performed on 89 patients with nephrologic diseases. Accurate diagnosis was reached in 93% of cases at the first biopsy, and the figure increased to 100% after a second biopsy. The use of 18 and 16 gauge needles allowed correct histological diagnosis in 95% of patients, and satisfactory histology in the extant 5%. US guidance and the use of 18 and 16 gauge needles reduced the complications related to renal biopsy: in fact, severe hematuria occurred in 2 cases only.