We performed conventional T2-weighted brain MRI examinations in six patients with multiple sclerosis (MS) and trigeminal neuralgia. In all patients brainstem lesions in positions expected to involve trigeminal fibers, particularly the entry zone of sensory fibers, were demonstrated. Compression of the trigeminal nerve by ectatic vessels, a recognized cause of idiopathic trigeminal neuralgia, was not observed. We conclude that in MS trigeminal neuralgia is usually caused by demyelinating lesions affecting pontine trigeminal pathways.