BACKGROUND: The relation between specific types of lumbosacral transitional vertebra and the degree of degeneration at and adjacent to the transitional level is unclear. It is further unknown whether the adjacent cephalad segment to a transitional vertebra is prone to greater degeneration than a normal L5/S1 level. PURPOSE: To evaluate the relation between specific lumbosacral transitional vertebra subtypes according to the Castellvi classification and the severity of degeneration at the transitional level and the adjacent cephalad segment. STUDY DESIGN: Retrospective review. PATIENT SAMPLE: 92 subjects with lumbosacral transitional vertebra grade 2 or higher and 94 controls without were retrieved from a PACS search. OUTCOME MEASURES: Disc degeneration parameters at the transitional and at the adjacent cephalad level. METHODS: After IRB approval, 92 (42 male; mean age 57±16 years) subjects with lumbosacral transitional vertebra grade 2 or higher and 94 (41 male; 51±16 years) controls without were retrieved from a PACS search. Degeneration of the last two segments of the lumbar spine was quantified using the Pfirrmann, and Modic classifications, along with documentation of annular tears, disc herniations and disc heights, and compared between the two groups. Further, L5/S1 levels of the controls were compared to the adjacent cephalad segments of the transitional vertebrae for the same parameters. RESULTS: While the controls at L5/S1 had moderate to severe degeneration by Pfirrmann grades (31%) and Modic changes (MC: 20%), compared, the discs at the transitional level of the lumbosacral transitional vertebra group demonstrated significant less degeneration (3% and 1%,each p<0.05). The adjacent cephalad segments of the lumbosacral transitional vertebra group showed significantly greater degeneration (Pfirrmann grade 5: 39%; MC: 30%) compared to the L4/5 level in controls (16%; 11%; each p<0.05). The severity of disc degeneration using all parameters correlated with the type of lumbosacral transitional vertebra. The degree of degeneration of L5/S1 in controls was similar to the adjacent cephalad segment in lumbosacral transitional vertebrae. CONCLUSION: Increasing mechanical connection of a lumbosacral transitional vertebra protects the disc at the transitional level and predisposes the adjacent cephalad segment to greater degeneration. The adjacent cephalad segment had comparable degree of degeneration as the L5/S1 level of controls.