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