Aphthous ulcers also known as recurrent aphthous ulcers, aphthous stomatitis, recurrent aphthous stomatitis [RAS], or canker sores; are a common oral mucosal disease. They are ulcerations with no known cause and a wide spectrum of severity and frequency of recurrence. Clinically, RAS has different presentations. It can consist of solitary or multiple ulcers, usually on the non-keratinized oral mucosa. It has been proposed that aphthous ulcerations represent an autoimmune reaction and may be precipitated by stress or hormonal changes. I will be discussing the importance of right diagnosis and monitoring with a specific scoring system. I will discuss as well the predisposing factors, the microorganisms implicated in aphthous ulcers as well as different treatment modalities for the pediatric patient. I will discuss the clinical presentation of this condition together with the current views on the aetiology and pathogenesis of the disease.