• Only four cases of chaismal syndromes caused by arteriovenous malformations (AVMs) have been reported. We have examined two patients with chiasmal dysfunction caused by an AVM. In one patient, the AVM was suspected only after angiography. However, the presence of an angioma of the lip might have been a clue to the diagnosis. In the other patient, seizures and pulsating proptosis led to the correct diagnosis before angiography was performed. This patient also had episodes of transient bilateral blindness, presumably caused by postictal states or by periodic shunting with ischemia (chiasmal steal).