Present studies evaluated the functions of thick and thin nerve fibers in carpal tunnel syndrome (CTS) to determine whether data of thin nerve fibers can add further information to the diagnosis of CTS. Measurements were performed in 22 patients and 16 age-matched control subjects. Motor and sensory nerve conduction, vibratory testing, thresholds of warmth and cold sensations, suprathreshold magnitude of pain and flare response, as well as sympathetic reflexes induced by noxious mechanostimulation were examined before and 1, 3, 6, 12, and 18 months after decompression of the median nerve. Nerve dysfunction in CTS was mainly indicated by the electrophysiological parameters of thick myelinated nerve fibers. Impairment of thin nerve functions in CTS and postoperative recovery was demonstrated by quantitative somatosensory thermotesting. In contrast, assessment of flare response and sympathetic reflexes using infrared thermography and photoplethysmography did not add further information for the diagnosis of CTS.