The presenting symptoms of renal arteriovenous malformations are usually gross hematuria and hypertension. Herein we present an unusual case of huge renal arteriovenous malformation without these signs, but with ultrasound picture mimicking simple parapelvic cyst. Other imaging test, including Duplex ultrasound, computerized tomography and aortography, demonstrated that vascular lesion. We suggest that Duplex ultrasound should accompany the routine renal ultrasound in order not to miss such cases, especially when the physical examination suggests intra-abdominal vascular lesion or bleeding.