The basic neuroanatomic and physiologic aspects of the sympathetic outflow to the limbs are reviewed and correlated with the somatic sensory dermatomes. The recent literature is considered. A thermocouple thermometer was used to test 30 normal patients and 87 patients with clinically proven nerve root lesions. Thermographic imaging of the sensory dermatome is not plausible, and thermography is not recommended for clinical documentation of painful conditions of the neck, back, or limbs.