Although diffuse idiopathic skeletal hyperostosis (DISH) is generally asymptomatic, in rare cases it involves multiple segments and can present with intervertebral pseudoarthrosis which requires treatment. We report a case of a 47-year-old female patient with intervertebral pseudoarthrosis and severe dynamic instability in the L4-5 intervertebral disc due to DISH and provide a brief review of literature. The patient developed severe lower back pain and intermittent claudication due to the instability in the only mobile part between multiple fused vertebrae from C7 to L4 and fusion segment from L5 to the ilium. We performed long-range posterior spinal and two-stage 360° fusion with L4-5 lateral interbody fusion. After the surgery the pain and intermittent claudication were improved and bony fusion was successful. Reports of intervertebral pseudoarthrosis in DISH with no history of trauma are extremely rare. We have only been able to find 5 cases. Compared to the previous reports, the present case describes a youngest patient, first case of female, and had the longest fusion due to DISH. Therefore, the patient required long-range fusion from T10 to the iliac bone in order to achieve adequate stabilization. Moreover, the present case is the first example of choosing a lateral interbody fusion, which provides even more robust consolidation.