We intended to verify whether the U.S. Coast Guard is properly reporting service members who are prohibited from possessing a firearm (“prohibited individuals”) to the Federal Bureau of Investigation (FBI). However, in comparing relevant databases with data into the National Instant Background Check System (NICS), We identified a number of issues that led us to question the reliability of the Coast Guard’s data. As a result, OIG cannot identify the full scope of prohibited individuals or verify that the Coast Guard properly reported prohibited individuals to the Federal Bureau of Investigation (FBI) and to Congress. Despite our concerns about the quality of Coast Guard’s data, OIG identified 210 service members who committed offenses that placed them in one of the categories of prohibited individuals. Of these 210, Coast Guard did not enter 16 service members (8 percent) into NCIS. This underreporting occurred because Coast Guard policy did not require attorneys to forward information about all individuals referred for trial by general court martial for reporting to the FBI. Additionally, Coast Guard’s reporting to the FBI is centralized, and does not allow investigators in field offices to have direct access to NICS. We made eight recommendations that will enhance Coast Guard’s reporting of prohibited individuals to the FBI. The Coast Guard concurred with the recommendations.