Arteriovenous fistulae(AVF) are well documented complications of percutaneous renal biopsy. Between August 1995 and April 1997, we prospectively studied 280 consecutive ultransound-guided percutaneous renal biopsies to evaluate the incidence of post-biopsy AVF and its natural course. All biopsies patients were monitored through a routine follow-up echo-color popple sonography at post-biopsy 1, 7, 14 and 30 days. The 28 patients(10%) out of 280 consecutive percutaneous renal biopses were diagnosed to have AVF. There was no differences in the incidence of AVF between native and transplanted kidney biopsy. Most AVF were small(<2cm) and caused minimal or no symptoms. AVF was accompanied with large hematoma(thickness above 2cm) was observed in 9 cases(53%) of 17 native kidneys and none in 10 transplanted kidneys. This difference was statistically significant(P=0.008). At follow-up, AVF resolved spontaneously in 24 cases(87%). In two patients(7.1%) required superselective arterial embolization, one develoved spontaneous rupture of AVF, and one had persistence of AVF over 12 months. We concluded that color Doppler sonography provides a good, non-invasive and safe method for diagnosis and follow up of post-biopsy AVF.