In a 43-year old female with neuralgia of the second and third branch of the trigeminal nerve, the diagnosis was made on the basis of clinical findings. After the patient was treated with 2 x 200 mg of carbamazepine, all initial symptoms resolved, which confirmed the diagnosis. To distinguish between idiopathic and secondary trigeminal neuralgia, magnetic resonance imaging was scheduled. This investigation showed an acoustic neuroma in the cerebellopontine angle. Without magnetic resonance imaging this benign tumour would be diagnosed in a much later stage and the patient would have suffered unnecessary co-morbidity. Due to the relatively high incidence of secondary trigeminal neuralgia, routine magnetic resonance imaging in patients with a trigeminal neuralgia is justifiable.