Purpose: Adjacent segment disease (ASD) is the development of symptomatic degenerative pathology at mobile segments above and/or below the index fusion level. A long-term complication of spinal fusion, it commonly presents as spondylodiscitis within a few months following surgery as a result of surgical site infection. In contrast, delayed ASD (>1 year) is rare and its pathophysiology poorly understood. Methodology: Case report of a 79-year-old female with back pain and proximal adjacent spondylodiscitis, 3 years following L1-4 lateral lumbar interbody fusion. A literature review for cases of delayed ASD was undertaken. Results: Patient presented due to 2 months of aching midline back pain. She had a complex spinal history with initial instrumentation 22 years ago with L4-5 PLIF which was further extended to L1-4 LLIF 3 years ago. Recent CT imaging and bone scan showcased increased inflammatory change at the T12/L1 end plates and penetration of L1 pedicle screw tip into T12/L1 vertebral disc. Serial imaging showcased progressive hyperlordosis since initial single-level fixation. Given improving back pain, independent mobility and stable dynamic imaging, decision for conservative management was made without diagnostic biopsy. She has been followed up 3-monthly with stable serial imaging and serum inflammatory markers. Conclusion: Delayed ASD is a rare pathology of lumbosacral fusion surgery. Pathophysiology is unclear, but likely attributed to altered biomechanical loading and dynamic arterial circulation and consequential subacute infection of adjacent segment endplates. Our case and literature highlight select cases of delayed ASD may be managed successfully through a conservative approach.