The function of thick and thin sensory nerve fibers after surgical decompression in carpal tunnel syndrome were evaluated using quantitative sensory testing (QST). The thin nerve fibers were studied using tests for thermal thresholds, and the thick myelinated fibers by vibrametry. The tests were performed before surgery and at 6 weeks, 4 and 10 months after surgery. The improvement of function in thin nerve fibers came within 6 weeks (P = 0.001). The improvement of function in thick myelinated fibers continued to improve until 4 months after the operation (P = 0.0001). This difference in the time course of the recovery indicates that the thick myelinated nerve fibers were more affected than the thin nerve fibers. The function of both type sensory nerve fibers did also improve in the fifth finger (P = 0.05). The function in thin nerve fibers worsened somewhat between 6 weeks and 4 months after surgery, possibly due to postoperative scar tissue.