Patients with trigeminal neuralgia and control subjects were compared in respect of several risk factors for trigeminal neuralgia, to determine if these risk factors were related more specifically to the anatomical divisions of the trigeminal nerve. The vertical location of the pain was strongly related to age at diagnosis. Non-Jewish religion was a risk factor primarily for trigeminal neuralgia of the lower face (any third-division involvement), whereas non-drinking and non-smoking were risk factors for trigeminal neuralgia of the upper face (no third-division involvement). The tendency for trigeminal neuralgia to occur on the right side of the face can be attributed mostly to the right-sided predominance of trigeminal neuralgia of the upper face. The epidemiological evidence suggests that different ætiological mechanisms may operate for trigeminal neuralgia of the lower face and upper face.