Adult patients aged >16 years attending the ED with cellulitis as the primary diagnosis will be consecutively recruited. Only patients who are deemed suitable for an oral antibiotic will be enrolled. Patients who require IV therapy will not be enrolled. Cellulitis may arise de novo, or from a recognised cause such as a wound or ulcer. In order to generate an externally valid clinical prediction rule, we will include all patients attending the ED with cellulitis, including those who may have already been commenced on oral antibiotics (for example, by their general practitioner).