The aim of this study was to compare the reliability and validity of the CARDS and French classification systems for lumbar DS. Between May 2013 and December 2016, 158 consecutive patients diagnosed with single-level lumbar DS were included in this study, and all underwent lumbar fusion. All patients underwent long-cassette standing anterioposterior and lateral radiographs of the spine preoperatively and postoperatively. The images were graded according to the CARDS and French classification systems by two orthopedic spinal surgeons and two orthopedic spinal fellows, independently. Clinical outcome measures used were the visual analog scale, Oswestry Disability Index, and the 36-Item Short Form Health Survey. Clinical data were collected before surgery and 1 year after surgery. A total of 146 patients were finally included in this study and followed up for at least 1 year. When grading using the CARDS system, the κ values for inter- and intraobserver reliability were 0.837 and 0.869, respectively, representing perfect agreement. The interobserver κ value for the French classification was 0.693 and the intraobserver κ value was 0.743, both representing substantial agreement. CARDS Type D patients have higher preoperative back pain scores and better improvement after surgery compared with non-Type D patients. Mean back and leg pain was worse in French Type 5 patients, while the most significant improvement was also seen in Type 5 patients after surgery. Both CARDS and French classification systems have acceptable reliability and validity. The CARDS system is easier to utilize and has better reliability. IV.