Objective: This study compares participants in randomized controlled trials (RCTs) (the Minimal Invasive Treatment [MinT] trials) to participants in a related observational study with regard to their low back pain (LBP) symptom course. Study Design and Setting: Eligible patients were diagnosed with chronic LBP originating from the facet joints (N = 615) or sacroiliac (SI) joints (N = 533) and were treated with radiofrequency denervation and an exercise program. Randomized patients were compared to patients in the related observational study who fulfilled all RCT eligibility criteria (observational group 1) and to patients who did not fulfill at least one of the RCT eligibility criteria (observational group 2). Outcomes were pain intensity, treatment success, and functional status over a 3-month period. Longitudinal mixed-model analyses and linear regression models were applied to analyze the differences in outcomes between the RCT and observational study groups. Results: No differences in symptom course were found between patients in the RCTs and patients in observational group 1. Patients with facet joint pain in observational group 2 had overall less treatment success (odds ratios [OR], 0.67; 95% confidence interval [CI], 0.50–0.90), and less improvement in physical functioning (mean difference [MD], 5.82; 95% CI, 2.54–9.11) compared to the RCT patients. Patients with SI joint pain in observational group 2 had higher pain scores (MD, 0.40; 95% CI, 0.09–0.72), less treatment success (OR, 0.72; 95% CI, 0.54–0.96), and less improvement in physical functioning (MD, 7.16; 95% CI, 3.84–10.47) compared to the RCT patients. Conclusion: This supports the generalizability of results from the MinT RCTs as this study suggests that these RCTs reflect clinical practice when comparing similar populations. To what extent this holds true for all RCTs in LBP should be further explored.