To characterize the Orthopaedic Trauma Association Open Fracture Classification (OTA-OFC) and Gustilo-Anderson classification of open extremity fractures and determine if there is meaningful alignment between these grading systems. Retrospective case series. Level I academic trauma center. Adult patients with at least 1 operatively treated open extremity fracture and surgeon-assigned OTA-OFC and Gustilo-Anderson classification. Frequency, distribution, and association measures of OTA-OFC category scores and Gustilo-Anderson classification types. Two thousand twenty-seven patients (mean age, 43.1 ± 17.5 years) with 2215 fractures were included. Gustilo-Anderson type I or II fractures (n = 961; 43%) most frequently had the least severe scores for all OTA-OFC categories. Type IIIA fractures (n = 978; 44%) were most often assigned intermediate scores for OTA-OFC Bone Loss (n = 564; 58%). Type IIIB fractures (n = 204, 9%) were most often assigned intermediate OTA-OFC Skin scores (n = 120; 59%). Type IIIC fractures (n = 72; 3%) were most often assigned the most severe OTA-OFC Arterial score (n = 60; 83%). In the multivariable model, OTA-OFC Contamination scores showed little association (β = 0.05; 95% confidence interval CI, 0.01-0.09) with Gustilo-Anderson classification severity. Conversely, higher OTA-OFC Arterial (β = 0.50; 95% CI 0.44-0.56) and Skin (β = 0.46; 95% CI, 0.40-0.51) scores were strongly associated with more severe Gustilo-Anderson classifications. OTA-OFC Contamination scores were weakly associated with Gustilo-Anderson classification severity for open fractures. The study findings suggest that the current Gustilo-Anderson classification does not adequately account for injury contamination, a known predictor of infection. Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.