Unsure about codes that payers are using for ABA services? This chart outlines the essential elements of ABA assessment and treatment services and the HCPCS and CPT® codes that have been used for reporting and billing those services. In particular, it shows the conversion of the Category III (temporary) CPT® codes that were issued in 2014 to the Category I and modified Category III codes that took effect on January 1, 2019. The accompanying letter provides additional important information about the 2019 code set.