In medical writing, quality control (QC) means ensuring that a document's content, style, and format are of high quality. This does not just ‘happen’ but is the result of a systemic QC review. These reviews are critical because mistakes can cause the reader to question the validity of the content and may lead to errors in interpretation. QC guidance documents may be available in-house or from a client, but if not available, they can be created by combining existing guidelines and checklists. A good QC review takes time but is well worth the effort.