We performed microscopic lumbar foraminotomy in all the patients diagnosed with degenerative lumbar foraminal stenosis (DLFS) and retrospectively reviewed the clinical outcomes and the factors influencing them. The preoperative Japanese Orthopaedic Association (JOA) score of 13.8 significantly improved to 21.9 postoperatively. Although leg pain reduced in 44 patients (95.7%) immediately after surgery, it recurred in 9 patients (19.6%). The recurrence frequency was significantly higher and the JOA score improvement ratios significantly lower in patients with degenerative lumbar scoliosis (DLS) than in those without DLS. Even among patients with DLS, those with <3° Cobb angle difference between the supine and standing positions showed satisfactory results, with no recurrence. In conclusion, microscopic lumbar foraminotomy for DLFS produced satisfactory clinical outcomes even in patients with DLS. However, the outcomes were poor in patients with unstable DLS.