Two-thirds of the world’s population lack access to safe anesthesia and surgical care. Nongovernmental organizations (NGOs) play an important role in bridging the gap, but surgical outcomes vary. After complex surgeries, up to 20-fold higher postoperative complication rates are reported and the reasons for poor outcomes are undefined. Little is known concerning the incidence of anesthesia complications. Mercy Ships uses fully trained staff, and infrastructure and equipment resources similar to that of high-income countries, allowing the influence of these factors to be disentangled from patient factors when evaluating anesthesia and surgical outcomes after NGO sponsored surgery. We aimed to estimate the incidence of anesthesia-related and postoperative complications during a 2-year surgical mission in Madagascar.As part of quality assurance and participation in a new American Society of Anesthesiologists Anesthesia Quality Institute sponsored NGO Outcomes registry, Mercy Ships prospectively recorded anesthesia-related adverse events. Adverse events were grouped into 6 categories: airway, cardiac, medication, regional, neurological, and equipment. Postoperative complications were predefined as 16 adverse events and graded for patient impact using the Dindo-Clavien classification.Data were evaluated for 2037 episodes of surgical care. The overall anesthesia adverse event rate was 2.0% (confidence interval [CI], 1.4-2.6). The majority (85% CI, 74-96) of adverse events occurred intraoperatively with 15% (CI, 3-26) occurring in postanesthesia care unit. The most common intraoperative adverse event, occurring 7 times, was failed regional (spinal) anesthesia that was due to unexpectedly long surgery in 6 cases; bronchospasm and arrhythmias were the second most common, occurring 5 times each. There were 217 postoperative complications in 191 patients giving an overall complication rate of 10.7% (CI, 9.3-12.0) per surgery and 9.4% (CI, 8.1-10.7) per patient. The most common postoperative complication was unexpected return to the operating room and the second most common was surgical site infection (39.2%; CI, 37.0-41.3 and 33.2%; CI, 31.1-35.3 of all complications, respectively). The most common (42.9%; CI, 40.7-45.1) grade of complication was grade II. There was 1 death.This study adds to the scarce literature on anesthesia outcomes after mission surgery in low- and middle-income countries. We join others in calling for an international NGO anesthesia and surgical outcome registry and for all surgical NGOs to adopt international standards for the safe practice of anesthesia.