<h3>BACKGROUND CONTEXT</h3> The elderly population, greater than 70 years old, is the fastest growing demographic in the U.S. Nearly 50% of individuals over 60 will experience lumbar spinal stenosis and 68% will develop scoliosis and adult spinal deformity (ASD). The octogenarian group, in particular, is considered at increased risk of complications following complex spine surgery. <h3>PURPOSE</h3> To assess the postoperative complications in order to determine the safety of MIS-ATP fusion in octogenarians. <h3>STUDY DESIGN/SETTING</h3> Retrospective case series. <h3>PATIENT SAMPLE</h3> A total of 43 patients with ASD who underwent MIS-ATP fusion surgery between January 2010 and December 2020. <h3>OUTCOME MEASURES</h3> The Charlson comorbidity index (CCI), American Society of Anesthesiologists (ASA), 30 days, one-year postoperative mortality. Demographic data included age, sex, BMI, number of fused segments, operation time, estimated blood loss, length of hospital stay, peri- and postoperative complications. <h3>METHODS</h3> A total of 43 patients with ASD who underwent surgery between January 2010 and December 2020 were retrospectively reviewed. Inclusion criteria were octogenarian adults (80-89 years old) with lumbar spinal deformity (scoliosis and/or kyphosis) treated with combined anterior (MIS-ATP) posterior (percutaneous fixation) fusion. The CCI was calculated, and outcomes measured were 30 days and one-year post-operative mortality. Demographic data included age, sex, BMI, number of fused segments, operation time, estimated blood loss, length of hospital stay, perioperative and postoperative complications. <h3>RESULTS</h3> A total of 43 patients were included for analysis in this study with an average age of 82.3 years old (range: 80-88 years). Of these, 24 patients were female (55.8%) and the average BMI was 28.0. Three patients (7.0%) were active smokers, 13 (30.2%) former smokers, 27 (62.8%) never smoked, and 7 patients (16%) reported alcohol consumption. The studied operative parameters (in averages) were: levels fused (3.9), operative time (3.1 hours), operative blood loss (412 cc) and length of hospital stay (7.5 days). Overall, the average CCI and ASA score were 5 and 3 respectively. Thirteen patients (30.2%) experienced complications (hardware-related, neurological, infectious and cardiovascular) of whom 6 (14.0%) required a revision surgery. No mortalities were noted at 30 days and at 1-year after surgery. Two patients died 2-3 years after surgery, from medical reasons unrelated to the spinal surgery. <h3>CONCLUSIONS</h3> This study highlights the relative safety of MIS-ATP surgery in the octogenarian population, despite the underlying medical vulnerability. Satisfactory recovery can still be achieved without major increase in operative morbidity and mortality. <h3>FDA DEVICE/DRUG STATUS</h3> Posterior longitudinal rod implants (Approved for this indication), Iliac screws (Approved for this indication), pedicle screws (Approved for this indication), interbody cage fusion (Approved for this indication).