It is sometimes helpful to characterize medical conditions as either structural (with abnormalities is specific anatomic structures that can be identified through organ-specific testing) and functional (when body parts are not communicating and coordinating physical processes appropriately even though all test results are normal). Some patients have both structural and functional disorders, concurrently; it is important to treat each cause of an adolescent’s symptoms. Chronic fatigue and chronic pain are common and often not linked to specific test abnormalities. Patients with dysfunction of the autonomic nervous system can have orthostatic intolerance and chronic fatigue; some have excessive postural tachycardia and qualify for a diagnosis of postural orthostatic tachycardia syndrome. All of these patients can respond favorably to specific changes in intake, activity, sleep, and mindset (with cognitive behavioral therapy). Sometimes, specific medications provide adjunctive benefits for pain and for postural orthostatic tachycardia syndrome. Clinicians can guide patients with functional disorders to good recovery.