Background Lumbar spinal stenosis (LSS) is a common degenerative condition of the spine that causes back pain radiating to the lower extremity. Surgical treatment is indicated to treat progressive radical symptoms. Obesity has been associated with inferior results in the domains of quality of life (QoL) following an LSS operation, but the research findings have been limited. This paper aims to identify whether obesity affects QoL due to back pain among patients who underwent an operation for LSS. Methods This study is based on a series of patients operated on for LSS between 2012 and 2018. Operated patients who returned for follow-up forms within the first or second years were included. A total of 359 patients were selected, 163 males (45%) and 196 females (55%). The mean age was 68.9 years. The EuroQol five-dimension scale (EQ-5D) questionnaire was chosen to measure QoL and the Oswestry Disability Index (ODI) for functional disability. Results QoL, as measured by EQ-5D, was preoperatively lower in those patients with a BMI ≥ 30. One year after the operation, all groups had a similar trend of improved QoL. At the second year, the results in all groups levelled off even though there was no statistical difference in clinical outcomes (p = 0.92). The ODI was preoperatively statistically higher in patients with a BMI ≥ 30 (p < 0.001). Two years after the surgery, all groups had improved ODI scores, but there was no statistical difference in ODI between the BMI groups (p = 0.54). Conclusion Surgical intervention for debilitating or longstanding symptoms of LSS should be considered as a treatment option for suitable patients in spite of an elevated BMI.