1. A method of treating a patient's neurological or psychiatric disorder, the method comprising: using a control module coupled to a first electrode and a second electrode to deliver electrical stimulation to a nervous system component through the first electrode and the second electrode to treat the patient's neurological or psychiatric disorder, said first electrode and said second electrode being implanted in the patient's body; monitoring impedance between the first electrode and the second electrode; automatically adjusting at least one parameter of the electrical stimulation to compensate for a monitored change of electrode impedance between the first electrode and the second electrode; and delivering a subsequent electrical stimulation with the at least one adjusted parameter to the nervous system component through the first electrode and the second electrode to treat the patient's neurological or psychiatric disorder.