The purpose of this report was to estimate the additional annual cost to the U.S. healthcare system attributable to preventable medication errors (MEs) in the operating room. The ME types were iteratively grouped by their associated harm (or potential harm) into 13 categories, and we determined the incidence of operations involving each ME category (number of operations involving each category/total number of operations): (1) delayed or missed required perioperative antibiotic (1.4% of operations); (2) prolonged hemodynamic swings (7.6% of operations); (3) untreated postoperative pain >4/10 (18.9% of operations); (4) residual neuromuscular blockade (2.9% of operations); (5) oxygen saturation <90% due to ME (1.8% of operations); (6) delayed emergence (1.1% of operations); (7) untreated new onset intraoperative cardiac arrhythmia (0.72% of operations); (8) medication documentation errors (7.6% of operations); (9) syringe swaps (5.8% of operations); (10) presumed hypotension with inability to obtain a blood pressure reading (2.2% of operations); (11) potential for bacterial contamination due to expired medication syringes (8.3% of operations); (12) untreated bradycardia <40 beats/min (1.1% of operations); and (13) other (13.0% of operations). Through a PubMed search, we determined the likelihood that the ME category would result in downstream patient harm such as surgical site infection or acute kidney injury, and the additional fully allocated cost of care (in 2021 U.S. dollars) for each potential downstream patient harm event. We then estimated the cost of the MEs across the U.S. healthcare system by scaling the number of MEs to the total number of annual operations in the United States (N = 19,800,000). The total estimated additional fully allocated annual cost of care due to perioperative MEs was $5.33 billion U.S. dollars.