OBJECTIVES:  To update Deyo’s International Classification of Disease, 9th revision, Clinical Modification (ICD-9) coding algorithm for Charlson Comorbidity Index (CCI) with corresponding ICD-10 codes and assess the concordance between algorithms using a large retrospective hospital administrative database. METHODS:  Deyo’s ICD-9 algorithm for CCI was updated referencing Quan’s modified version of Deyo’s algorithm and clinical judgment made by the Premier team. The ICD-10 algorithm for CCI was developed using the mapped ICD-10 codes based on the Centers for Medicare and Medicaid Services (CMS) 2016 General Equivalence Mappings, with further adjustment according to the 2016 CMS ICD-10 codes tabular list. The ICD-10 algorithm was validated by a concordance analysis using data from hospitals that submitted both ICD-9 and ICD-10 data to the Premier Healthcare Database during Quarter 4 of 2015. Descriptive analysis was conducted to compare the distribution of CCI scores and prevalence for the individual conditions between the two algorithms. Concordance was assessed by Kappa statistics calculated for each of the CCI comorbidities. RESULTS:  The analysis included CONCLUSIONS:   The ICD-10 CCI score had excellent concordance with the ICD-9 algorithm and both algorithms are available for use in outcome studies.