© 2017 Background: The Organ Procurement Transplant Network (OPTN) registry collects data on posttransplant malignancies in solid organ transplant recipients. Complete and accurate registry data on skin cancer is critical for research on epidemiology and interventions. Objective: The study goal was to determine the validity of Organ Procurement Transplant Network skin cancer data. Methods: This cohort study compared reporting of posttransplant squamous cell carcinoma (SCC) and malignant melanoma (MM) in OPTN to medical-record review-derived data from the Transplant Skin Cancer Network (TSCN) database. In total, 4934 organ transplant recipients from the TSCN database were linked to patient-level OPTN malignancy data. We calculated sensitivity, specificity, correct classification (CC), positive predictive value (PPV), and negative predictive value (NPV) for SCC and MM reporting in the OPTN database. Results: OPTN reporting for SCC (population prevalence 11%) had sensitivity 41%, specificity 99%, PPV 88%, NPV 93%, and CC 93%. OPTN reporting for MM (population prevalence 1%) had sensitivity 22%, specificity 100%, PPV 73%, NPV 99%, and CC 99%. Limitations: Only a subset of patients in the TSCN cohort had matched United Network for Organ Sharing cancer registry data for comparison. Conclusion: OPTN reporting had poor sensitivity but excellent specificity for SCC and MM. Dermatologists and transplant physicians are encouraged to improve the validity of OPTN skin cancer data through improved communication and reporting.