Radiographic analysis was performed retrospectively. Outcomes and complications were collected prospectively. To assess complications after posterior fusion and instrumentation for degenerative lumbar scoliosis, to determine risk factors of complications, and to analyze the clinical outcomes of surgery. The complications after degenerative lumbar scoliosis surgery have reported to be high. Risk factors for developing complications are unknown. Forty-seven patients (average age, 66.6 years; range, 48-83 years) with degenerative lumbar scoliosis undergoing posterior fusion and instrumentation were analyzed. Seven patients had additional posterior lumbar interbody fusion at the lumbosacral junction. The average number of levels fused was 4.7 +/- 2.2 segments. We evaluated the early perioperative (<3 months after surgery) and late complications. There were 14 early perioperative complications and 18 late complications. There was 1 case of mortality by pulmonary embolism. Early complications included ileus, urinary tract infection, transient delirium, superficial infection, and neurologic deficit. Late complications included adjacent segment diseases, pseudarthrosis, and loosening of screws. Adjacent segment disease developed at the proximal segment in 10 patients and at the distal segment in 5 patients. Pseudarthrosis was noted at the lumbosacral junction in 2 patients. Revision surgery was performed in 7 patients. Older patients (>65 years) had the tendency to increase early complications without statistical difference (P = 0.053). Excessive intraoperative blood loss was the most significant risk factor for the development of early perioperative complications, and number of levels fused was related to blood loss. Operative time and multiple medical comorbidities were not associated with higher complication rate. There were no specific factors related to the development of late complications. The complication rate after posterior fusion and instrumentation for degenerative lumbar scoliosis was 68%. Abundant blood loss was a significant risk factor for early perioperative complications. The improvement of Oswestry disability index was less in patients with late complications.