For some people recurrent mouth sores (apthous stomatitis) can be the sole indicator of celiac disease.
Cankier sores are painful white or yellow open ulcers surrounded by a bright red area. They can be caused by a break in the mucous membrane lining of the mouth or upper throat as a result of stress, viral infections, food allergies, and other conditions.
Canker sores are also a common finding in gluten sensitivity and for some people, they're the only predominant symptom.
Source: Celiac Disease Foundation Newsletter, June, 2009.