Introduction  Sagittal spinopelvic alignment (SSPA) parameters are essential for the diagnosis of adult spinal deformities and their progression. Certain clinical symptoms that occur in patients with lumbar spinal stenosis (LSS) and herniated nucleus pulposus (HNP) may distort one’s SSPA and mimic adult spinal deformities. Inaccurate measurements of SSPA may lead to unnecessary realignment surgeries, which is an enormous burden to both physicians and patients. In this study, we aimed to differentiate SSPA in symptomatic patients to those without symptoms in the standing position.   Methods   This retrospective cohort study evaluated the changes in SSPA following simple lumbar decompression surgery in patients with LSS and HNP. Relative sagittal alignment (RSA), relative pelvic version, relative lumbar lordosis (RLL), lordosis distribution index (LDI), and global alignment and proportion (GAP) scores were calculated using the conventional Schwab classification method. First, the pre- and postoperative SSPA parameters were compared. Second, patients were sub-grouped into symptomatic (SP) and asymptomatic (SN) groups on standing position. Patients with pain that is evoked by standing for longer than 10 minutes were defined as symptomatic, which corresponds to 4 points or more on the ODI subcategory - 'standing'. SSPA parameter changes after symptom relief in SP group following simple lumbar decompression surgery were compared to those of SN group.   Results   Sixty-three patients who underwent simple lumbar decompression between April 2019 and June 2021 were included in this study. Thirty-three and 29 patients were grouped into the SP and SN group, respectively. The mean age, BMI, male-to-female ratio, and diagnosis of lumbar pathology were not significantly different between the two groups (p=.68, p=.82, p=076, and p=.80, respectively). In total, patients with lumbar pathology showed improvements in all SSPA parameters following surgery (RSA, RLL, and LDI values improved with p=.002, p<.001, and p=.002, respectively). However, after subgrouping, asymptomatic patients in the standing position did not show significant SSPA alterations except for LDI (p=.035), whereas symptomatic patients significantly improved in terms of their RSA, RLL, LDI, and GAP values (p=.001, p<.001, p=0.032, and p=0.05, respectively) following symptom relief from the surgery.   Discussion   Our study demonstrated that patients with pain on standing within 10 minutes showed significant correction in RSA, RLL, and GAP values following simple lumbar decompression, whereas patients without pain on standing did not. Furthermore, SN group, scoring 3 or less on the ODI subcategory 'standing', scored higher VAS - leg and back - and total ODI compared to SP group. Therefore, misleading measurements of SSPA is more likely caused by the pain on standing position and not by other symptoms relating to LSS and HNP.       Previous studies have reported that SSPA improvements were observed in LSS patients who have undergone simple lumbar decompression surgeries. Most presumed buckling of ligamentum flavum impinging on spinal nerves caused distortion of SSPA, as flexion of lumbar spine may release the impingement. However, these studies provided limited evidence on improvements of SSPA and showed various patterns of improvements. Based on our study, it is important to focus on clinical symptoms rather than disease entity itself.