A post-biopsy arteriovenous (AV) fistula in a renal allograft was diagnosed using color-coded Doppler sonography. Because the patient was asymptomatic, no specific treatment was initiated. 15 months after the diagnosis was established, severe hematuria with obstruction of the bladder occurred. Angiography revealed a connection of the fistula to the renal pelvis. The patient was treated successfully by transarterial embolization of the fistula. As a conclusion, we suggest periodical follow-up examinations of asymptomatic AV fistulas in renal allografts using color-coded Doppler sonography during 3–6 months. When no spontaneous regression of the fistula can be observed, embolization therapy should be performed even when the fistula is asymptomatic, in order to prevent late onset of complications.