BACKGROUND CONTEXT Lumbar isthmic spondylolisthesis has been reported to occur in 4% to 6% of the population. The prevalence of L5-S1 degenerative spondylolisthesis has not been reported to date. Large series evaluating prevalence of congenital or degenerative conditions of the lumbar spine are needed in order to advise patients in clinical practice and to guide future research questions. PURPOSE To evaluate the prevalence of isthmic and degenerative spondylolisthesis in patients undergoing abdominal/pelvic CT scans. STUDY DESIGN/SETTING Observational study. PATIENT SAMPLE Patients undergoing CT scans of the abdomen and pelvis at a Level I trauma center in January 2017. OUTCOME MEASURES Presence or absence of isthmic/degenerative spondylolisthesis. METHODS Patients undergoing CT scans of the abdomen and pelvis at a Level I trauma center in January 2017 were enrolled. Inclusion criteria included complete CT scans (axial sagittal, coronal). The following variables were collected: age, sex, race/ethnicity as well as the presence of L3-L4, L4-L5, L5-S1 isthmic spondylolisthesis and the presence of L3-L4, L4-L5, L5-S1 degenerative spondylolisthesis. RESULTS One thousand CT scans were available and 882 patients met our inclusion criteria: 440 F (49.9%) and 442 M with an average age of 57.1 (SD 18.8). Ethnicities represented was 1.1% Asian-Americans, 14.3% African-Americans, 83.7% Caucasians and 4% Hispanic. The prevalence of isthmic spondylolisthesis was 6.8%; L3-L4 (0.9%), L4-L5 (2.2%), L5-S1 (3.7%). The prevalence of degenerative spondylolisthesis was 24.8%; L3-L4 (4.5%), L4-L5 (12%), L5-S1 (8.3%). CONCLUSIONS In one of the largest series evaluating the prevalence of isthmic and degenerative lumbar spondylolisthesis, we have identified the prevalence of L5-S1 isthmic spondylolisthesis to be 3.7%. The prevalence of L5-S1 degenerative spondylolisthesis has not been described to date and has a prevalence of 8.3%. Overall, L4-L5 had the highest prevalence of degenerative spondylolisthesis at 12%. This study can guide patient care by providing prevalence information and can guide future research on rarely described conditions such as L5-S1 degenerative spondylolisthesis. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. Lumbar isthmic spondylolisthesis has been reported to occur in 4% to 6% of the population. The prevalence of L5-S1 degenerative spondylolisthesis has not been reported to date. Large series evaluating prevalence of congenital or degenerative conditions of the lumbar spine are needed in order to advise patients in clinical practice and to guide future research questions. To evaluate the prevalence of isthmic and degenerative spondylolisthesis in patients undergoing abdominal/pelvic CT scans. Observational study. Patients undergoing CT scans of the abdomen and pelvis at a Level I trauma center in January 2017. Presence or absence of isthmic/degenerative spondylolisthesis. Patients undergoing CT scans of the abdomen and pelvis at a Level I trauma center in January 2017 were enrolled. Inclusion criteria included complete CT scans (axial sagittal, coronal). The following variables were collected: age, sex, race/ethnicity as well as the presence of L3-L4, L4-L5, L5-S1 isthmic spondylolisthesis and the presence of L3-L4, L4-L5, L5-S1 degenerative spondylolisthesis. One thousand CT scans were available and 882 patients met our inclusion criteria: 440 F (49.9%) and 442 M with an average age of 57.1 (SD 18.8). Ethnicities represented was 1.1% Asian-Americans, 14.3% African-Americans, 83.7% Caucasians and 4% Hispanic. The prevalence of isthmic spondylolisthesis was 6.8%; L3-L4 (0.9%), L4-L5 (2.2%), L5-S1 (3.7%). The prevalence of degenerative spondylolisthesis was 24.8%; L3-L4 (4.5%), L4-L5 (12%), L5-S1 (8.3%). In one of the largest series evaluating the prevalence of isthmic and degenerative lumbar spondylolisthesis, we have identified the prevalence of L5-S1 isthmic spondylolisthesis to be 3.7%. The prevalence of L5-S1 degenerative spondylolisthesis has not been described to date and has a prevalence of 8.3%. Overall, L4-L5 had the highest prevalence of degenerative spondylolisthesis at 12%. This study can guide patient care by providing prevalence information and can guide future research on rarely described conditions such as L5-S1 degenerative spondylolisthesis.