The incidence of neonatal abstinence syndrome (NAS), a withdrawal syndrome associated with prenatal opioid or other substance exposure (1), has increased as part of the U.S. opioid crisis (2). No national NAS surveillance system exists (3), and data about the accuracy of state-based surveillance are limited (4,5). In February 2018, the Pennsylvania Department of Health began surveillance for opioid-related NAS in birthing facilities and pediatric hospitals* (6). In March 2019, CDC helped the Pennsylvania Department of Health assess the accuracy of this reporting system at five Pennsylvania hospitals. Medical records of 445 infants who possibly had NAS were abstracted; these infants had either been reported by hospital providers as having NAS or assigned an International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) hospital discharge code potentially related to NAS.† Among these 445 infants, 241 were confirmed as having NAS. Pennsylvania's NAS surveillance identified 191 (sensitivity = 79%) of the confirmed cases. The proportion of infants with confirmed NAS who were assigned the ICD-10-CM code for neonatal withdrawal symptoms from maternal use of drugs of addiction (P96.1) was similar among infants reported to surveillance (71%) and those who were not (78%; p = 0.30). Infants with confirmed NAS who were not assigned code P96.1 typically had less severe signs and symptoms. Accurate NAS surveillance, which is necessary to monitor changes and regional differences in incidence and assist with planning for needed services, includes and is strengthened by a combination of diagnosis code assessment and focused medical record review.