Most people with recurrent aphthous ulcers develop a few ulcers less than 1 cm in diameter, that heal after 5-14 days without scarring. The causes are unknown, but risks of recurrence may decrease if the person gives up smoking. Local physical trauma may trigger ulcers in susceptible people. In 10% of sufferers, lesions are more than 1 cm in diameter, and can cause scarring.We conducted a systematic review and aimed to answer the following clinical question: What are the effects of treatments for recurrent aphthous ulcers? We searched: Medline, Embase, The Cochrane Library and other important databases up to August 2006 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).We found 18 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.In this systematic review we present information relating to the effectiveness and safety of the following interventions: analgesics (local), carbenoxolone mouthwash, chlorhexidine (and similar agents), corticosteroids (topical), and tetracycline antibiotic mouthwash.