PURPOSE: To evaluate the usefulness and complications of renal biopsy under ultrasonography-guidance in renal dysfunction after renal transplantation. MATERIALS AND METHODS: Ultrasonography-guided renal biopsy was done in 47 patients with the transplanted kidney. The subjects consisted of 30 males and 17 females, age ranged from 16 to 66 years (average age = 38 years). Biopsies were done once in 27 patients, twice in 17 patients, three times in 3 patients, a total of 70 biopsies. The success rate of renal biopsy for the accurate pathologic diagnosis and the incidence and types of complications following biopsy were evaluated. RESULTS: The success rate of renal biopsy for the accurate pathologic diagnosis was 96%(67/70). Pathologic diagnosis included 27 cases of acute rejection(39%), 8 cases of acute tubular necrosis(11%), 4 cases of acute rejection and acute tubular necrosis(6%), 4 cases of cyclosporin toxicity(6%), 4 cases of primary disease recurrence(6%), 4 cases of infection(6%) and others. Complications after renal biopsy included 15 cases of microscopic hematuria(21%), 1 case of gross hematuria with spontaneous cessation and 1 case of life threatening hemorrhage. CONCLUSION: Ultrasonography-guided renal biopsy is a safe and effective diagnostic method for the evaluation of renal dysfunction following renal transplantation.