Diagnostic errors are relatively common in general practice. Paul Silverston describes a mnemonic-based system to prevent and detect these errors Diagnostic errors in primary care are relatively common and they have the potential to cause serious harm to patients. Up to 80% of these errors are believed to be preventable. This article describes a mnemonic-based system that practice nurses can use to prevent diagnostic errors from arising, as well as to detect these errors when they occur. The mnemonic is designed to be used pre-consultation to reduce the risk of errors arising through better preparation; during the consultation, as a diagnostic error checklist; and after the consultation to encourage reflective practice and critical thinking.