Methods for treating medical disorders, such as migraine or other primary headaches, or fibromyalgia, by electrical stimulation of a nerve. The method comprises applying a stimulus to a patient having a medical condition and measuring a baseline physiological response from the patient. An electrical impulse is applied to a nerve within the patient and the response evoked by the electrical impulse is measured and compared to the first baseline physiological response. The methods may be used to optimize the placement of a stimulator, to test whether a patient is a suitable candidate for treatment using nerve stimulation, and/or to select the stimulation parameters that optimize acute or chronic treatment.