Background There are no diagnostic support tools composed of a simple, single-sheet, self-administered, self-reported history questionnaire (SSHQ) for patients with leg symptoms caused by either lumbar spinal stenosis (LSS) or lumbar disc herniation (LDH), at the same time, can discriminate the two diseases. Methods We conducted retrospective and prospective derivation studies and a prospective validation study. Based on data from 137 patients with LSS and 206 with LDH, we identified key prediction factors to establish the diagnosis of LSS and LDH, which became the basis of a temporary SSHQ. Next, we performed a prospective derivation study in which 296 patients with LSS or LDH completed preoperatively this temporary SSHQ. After univariate and multivariate analyses of each question, questions on both diseases in addition to age factor were selected, providing the final version of the SSHQ. A validation study was subsequently performed with 342 consecutive patients with leg symptoms. The sensitivity, specificity and likelihood ratio of this SSHQ were calculated to determine the cut-off points for LSS and LDH. Results A SSHQ with 15 questions was developed from retrospective and prospective derivation studies. The score of each question was weighted based on the multivariate analysis and then, it was approximated to integer value. According to assessment of the discriminatory performance of the clinical prediction rule of the SSHQ, the cut-off point for LSS was ≥13 and that for LDH was ≥11. The sensitivity, specificity, and positive and negative likelihood ratios of this SSHQ at those cut-off points were, respectively, 92.7%, 84.7%, 6.07, and 0.09 for LSS, and 91.0%, 85.2%, 6.15, and 0.11 for LDH. Conclusions This is the first report of a diagnostic support tool for patients with LSS- or LDH-induced leg symptoms combined in a single SSHQ that could help establish diagnosis of the two diseases in the daily clinical practice.