We present the case of a 57-year-old man who developed retroperitoneal hemorrhage due to unintentional arterial puncture during femoral artery cannulation for Guglielmi detachable coil embolization. On emergence from anesthesia, he developed severe hypotension. Computed tomographic angiogram of the abdomen showed retroperitoneal hematomas around the urinary bladder, liver, and spleen. Because femoral artery cannulation is a common procedure for intravascular embolization in neuroradiologic procedures, Clinicians should be aware of the development of severe hematomas as a consequence of femoral artery puncture.