File review research benefits from the work of others by analyzing previously collected data. File review research can be especially beneficial when researching hidden and vulnerable populations such as child sex trafficking victims. This research method case review highlights some of the benefits and limitations of file research. We also cover how to gain access to files, how to cross-validate the file data with expert interviews, how to handle unexpected setbacks, and how to manage nonstandard file content. In summary, file review research makes use of a wealth of excellent and underutilized data without expending excessive amounts of time or money and without jeopardizing vulnerable populations.