OBJECTIVE The Timed Up and Go (TUG) test is a simple, objective, and standardized method to measure objective functional impairment (OFI) in patients with lumbar degenerative disc disease (DDD). The objective of the current work was to validate the OFI baseline severity stratification (BSS; with levels of "none," "mild," "moderate," and "severe"). METHODS Data were collected in a prospective IRB-approved 2-center study. Patients were assessed with a comprehensive panel of scales for measuring pain (visual analog scale [VAS] for back and leg pain), functional impairment (Roland-Morris Disability Index [RMDI] and Oswestry Disability Index [ODI]), and health-related quality of life (HRQOL; EQ-5D and SF-12). OFI BSS was determined using age- and sex-adjusted cutoff values. RESULTS A total of 375 consecutive patients scheduled for lumbar spine surgery were included. Each 1-step increase on the OFI BSS corresponded to an increase of 0.53 in the back pain VAS score, 0.69 in the leg pain VAS score, 1.81 points in the RMDI, and 5.93 points in the ODI, as well as to a decrease in HRQOL of -0.073 in the EQ-5D, -1.99 in the SF-12 physical component summary (PCS), and -1.62 in the SF-12 mental component summary (MCS; all p < 0.001). Patients with mild, moderate, and severe OFI had increased leg pain by 0.90 (p = 0.044), 1.54 (p < 0.001), and 1.94 (p < 0.001); increased ODI by 7.99 (p = 0.004), 12.64 (p < 0.001), and 17.13 (p < 0.001); and decreased SF-12 PCS by -2.57 (p = 0.049), -3.63 (p = 0.003), and -6.23 (p < 0.001), respectively. CONCLUSIONS The OFI BSS is a valid measure of functional impairment for use in daily clinical practice. The presence of OFI indicates the presence of significant functional impairment on subjective outcome measures.