INTRODUCTION: Studies have previously reported higher complication rates in elective total joint arthroplasty (TJA) for nonagenarians compared with younger cohorts. The purpose of this study was to assess whether nonagenarians were still at increased risk of complications and hospital readmissions by answering three questions: (1) Do nonagenarians have an increased risk of medical complications after TJA compared with octogenarians and septuagenarians? (2) Do nonagenarians have an increased risk of surgical complications after TJA compared with octogenarians and septuagenarians? (3) Do nonagenarians have an increased risk of hospital readmission after TJA compared with octogenarians and septuagenarians? METHODS: A total of 174 patients undergoing primary TJA between 2010 and 2017 were included; 58 nonagenarians (older than 90 years) were matched with 58 octogenarians (age 80 to 84 years) and 58 septuagenarians (age 70 to 74). Groups were matched by sex, diagnosis, surgeon, surgical joint, and year of surgery. Within each group, 31 patients (53%) underwent total hip arthroplasty and 27 patients (47%) underwent total knee arthroplasty. Comorbidities, American Society of Anesthesiologists physical status scores, and Charlson Comorbidity Index scores were captured preoperatively. Complications and readmissions occurring within 90 days postoperatively were evaluated. RESULTS: Nonagenarians had the highest rate of medical complications (33%) compared with octogenarians (14%) and septuagenarians (3%) (P < 0.001). Rates of surgical complications were not statistically different among nonagenarians (12%), octogenarians (9%), and septuagenarians (10%) (P = 0.830). Rates of hospital readmission were highest in nonagenarian patients (11%), but not statistically different compared with octogenarians (5%) or septuagenarians (2%) (P = 0.118). CONCLUSION: Nonagenarians were 3.1 times more likely to have a complication after TJA. The incidence of medical complications was highest in nonagenarians compared with octogenarians and septuagenarians, but rates of orthopaedic complications were similar. Nonagenarians who elect to proceed with TJA should be informed that they have an increased risk of postoperative medical complications compared with younger patients undergoing the same operation. LEVEL OF EVIDENCE: Level III, Therapeutic Study.