Study design This was a retrospective analysis of patient-reported outcomes across a two-year period. Summary of background data Patients suffering from lumbar stenosis may experience low back pain, neurogenic claudication, and weakness. Patients can benefit from surgical intervention, including decompression with or without fusion. However, the superiority of any single fusion construct remains controversial. Objective The goal of this study was to compare Patient-Reported Outcomes Measurement Information System (PROMIS®) Computer Adaptive Testing (CAT) measures in patients with lumbar spinal stenosis treated surgically with lumbar decompression and fusion with or without interbody fusion. Methods A retrospective review of patients with lumbar stenosis undergoing lumbar decompression and one-level fusion was performed. PROMIS® CAT Physical Function (PF) and Pain Interference (PI) assessments were administered using a web-based platform pre and postoperatively. Results Sixty patients with lumbar stenosis undergoing one-level lumbar fusion were identified. Twenty-seven patients underwent posterior lumbar fusion (PSF) alone and 33 underwent one-level lumbar interbody fusion (IF). Patients undergoing IF had better absolute PF scores compared to patients undergoing PSF at one-year postoperatively (48.9 v 41.6, p=0.002) and greater relative improvement in PF scores from baseline at one-year postoperatively (D13.6 v D8.6, p=0.02). A subgroup analysis of patients undergoing TLIF v PSF showed better absolute PF scores at the one-year follow-up in the TLIF group (47.1 v 42.3, p=0.04). No differences were found in PI scores at any time point between the PSF and IF groups. Patients undergoing IF had significantly shorter hospital stays (2.5 v 3.3 days, p=0.02) compared to patients undergoing PSF. Conclusions Patients with lumbar spinal stenosis treated with one-level IF reported higher absolute PF scores and experienced greater relative improvement in PF scores from baseline at one-year follow-up compared to patients treated with PSF alone. Additionally, IF is associated with a decreased length of hospital stay as compared to PSF.