CONTEXT:For patients with lumbar disk herniation, the Spine Patient Outcomes Research Trial (SPORT) randomized trial intent-to-treat analysis showed small but not statistically significant differences in favor of diskectomy compared with usual care. However, the large numbers of patients who crossed over between assigned groups precluded any conclusions about the comparative effectiveness of operative therapy vs usual care. OBJECTIVE:To compare the treatment effects of diskectomy and usual care. DESIGN, SETTING, AND PATIENTS:Prospective observational cohort of surgical candidates with imaging-confirmed lumbar intervertebral disk herniation who were treated at 13 spine clinics in 11 US states and who met the SPORT eligibility criteria but declined randomization between March 2000 and March 2003. INTERVENTIONS:Standard open diskectomy vs usual nonoperative care. MAIN OUTCOME MEASURES:Changes from baseline in the Medical Outcomes Study Short-Form Health Survey (SF-36) bodily pain and physical function scales and the modified Oswestry Disability Index (American Academy of Orthopaedic Surgeons/MODEMS version). RESULTS:Of the 743 patients enrolled in the observational cohort, 528 patients received surgery and 191 received usual nonoperative care. At 3 months, patients who chose surgery had greater improvement in the primary outcome measures of bodily pain (mean change: surgery, 40.9 vs nonoperative care, 26.0; treatment effect, 14.8; 95% confidence interval, 10.8-18.9), physical function (mean change: surgery, 40.7 vs nonoperative care, 25.3; treatment effect, 15.4; 95% CI, 11.6-19.2), and Oswestry Disability Index (mean change: surgery, -36.1 vs nonoperative care, -20.9; treatment effect, -15.2; 95% CI, -18.5. to -11.8). These differences narrowed somewhat at 2 years: bodily pain (mean change: surgery, 42.6 vs nonoperative care, 32.4; treatment effect, 10.2; 95% CI, 5.9-14.5), physical function (mean change: surgery, 43.9 vs nonoperavtive care 31.9; treatment effect, 12.0; 95% CI; 7.9-16.1), and Oswestry Disability Index (mean change: surgery -37.6 vs nonoperative care -24.2; treatment effect, -13.4; 95% CI, -17.0 to -9.7). CONCLUSIONS:Patients with persistent sciatica from lumbar disk herniation improved in both operated and usual care groups. Those who chose operative intervention reported greater improvements than patients who elected nonoperative care. However, nonrandomized comparisons of self-reported outcomes are subject to potential confounding and must be interpreted cautiously. TRIAL REGISTRATION:clinicaltrials.gov Identifier: NCT00000410.