BACKGROUND: The Timed Up and Go (TUG) test is a reliable tool for evaluating objective functional impairment (OFI) in patients with degenerative disc disease before a surgical intervention. The aim of this study is to assess the validity of the TUG test to measure change in function postoperatively. METHODS: In a prospective two-center study, OFI was assessed by the TUG test in patients scheduled for lumbar spine surgery, as well as 3 days (D3) and 6 weeks (W6) postoperatively. At each time point, the TUG test results were correlated with established subjective measures of pain intensity (visual analogue scale (VAS) for back and leg pain), functional impairment (Oswestry Disability Index (ODI)) and health-related quality of life (HRQoL; Short Form-12 (SF12)). RESULTS: The patient cohort comprised 136 patients with a mean age of 57.7 years; 76 were males, 54 had a microdiscectomy for lumbar disc herniation, 58 a decompression for a lumbar spinal stenosis, 24 had a surgical fusion procedure. The mean OFI t-score was 125.1 before surgery, and as patients improved on the subjective measures in the postoperative interval, the OFI t-score likewise decreased to 118.8 (D3) and 103.4 (W6). The Pearson correlation coefficient (PCC) between the OFI t-score and VAS leg pain was 0.187 preoperatively (p = 0.029) and 0.252 at W6 (p = 0.003). The PCC between OFI t-score and the ODI was 0.324 preoperatively (p < 0.001) and 0.413 at W6 (p < 0.001). The PCC between OFI t-score and physical HRQoL (SF12) was -0.091 preoperatively (p = 0.293) and -0.330 at W6 (p < 0.001). CONCLUSIONS: The TUG test is sensitive to change, and reflects the postoperative functional outcome even more exact than preoperatively, as indicated by better correlation coefficients of the OFI t-score with subjective measures of pain intensity, functional impairment and HRQoL.