One of the most fundamental concepts in medicine is that our ability to prescribe the correct medication is based upon our ability to make the correct diagnosis first. However, the relationship between illness, time and clinical assessment often means that the initial diagnosis may either be uncertain or incorrect. In addition, a patient may experience a serious complication of what is normally a minor illness. The dynamic and unpredictable nature of illness needs to be managed safely through the provision of safety-netting advice. However, it is essential that the medical content of that advice covers the specific medical criteria that would require a patient to seek a medical re-assessment of their symptoms and of their diagnosis. This article describes a mnemonic to help facilitate the development of symptom-based, patient safety-focused, safety-netting advice.