ObjectiveThe present retrospective study was performed to assess the anatomical features of the pedicle in isthmic spondylolisthesis and to correlate this with degree of slip.MethodsTwenty‐six patients with isthmic spondylolytic spondylolisthesis were studied. Relevant patient variables, length, width, height of the L5 pedicle, and the product of height and angle between pedicle and vertebral midline were measured. The length of the posterior compartment of the pedicle was calculated as the product of the pedicle length and angle.ResultsWith measurements comparable to those reported in previous publications, the L5 pedicle was found to be longer, and the height and width of the body shorter, than published values for patients without spondylolysis. The difference between the length of the posterior compartment of the pedicle and height of body is significantly proportional to the degree of slip and may reflect an adaptive response for stabilizing the vertebral body with posterior elements.ConclusionsThe pedicle anatomy was found to be altered in patients with L5S1 spondylolytic spondylolisthesis. These anatomical changes have implications for surgeons performing fusion operations in terms of length of screw, landmarks used and entry approach.