AIM: To evaluate clinical outcomes, complications, and pathological distribution in patients with lumbar disc herniation (LDH) and/or lumbar spinal stenosis (LSS) undergoing unilateral biportal endoscopic (UBE) surgery. MATERIAL and METHODS: This retrospective study included 127 patients with LDH and/or LSS who underwent UBE surgery between October 2024 and May 2025. Demographic and operative data were reviewed. Clinical outcomes were evaluated using Visual Analog Scale (VAS) scores at baseline, on postoperative Day 1, and at three months, and by using Oswestry Disability Index (ODI) scores at baseline and at three months. The primary outcome was the change in ODI from baseline to three months. Secondary outcomes included trajectories of VAS-leg/back, operative metrics, and complications. RESULTS: Of the patients, 58.3% were female and 41.7% were male with a mean age of 49.20±13.92 years. The mean operative time was 48.76±14.18 min, and 94.5% were discharged within one day. The most common pathology was pure disc herniation (63%), predominantly at the L4-L5 level (59.8%). Complication rates were as follow: dural tear in 3.9%, wound discharge in 2.4%, and recurrence in 3.2%. Statistically significant improvements in VAS and ODI scores were observed postoperatively (p<0.001). Moreover, minimum clinically important difference (MCID)-based responder rates were high for both disability and pain outcomes at three months, indicating that the improvements were also clinically meaningful. CONCLUSION: The UBE technique is associated with shorter operative time and length of hospital stay. This finding supports its place as effective and safe minimally invasive treatment for LDH and LSS, facilitating rapid functional recovery and early discharge.