The most common pathologic alterations seen by dentists are oral mucosal ulcerations, particularly those related to the herpes simplex virus and those produced by the autoimmune phenomenon known as recurrent aphthous stomatitis. Because the general frequency and clinical similarity of these conditions often make it difficult to distinguish one from the other, therapeutic intervention may be inappropriate. An improved understanding of the virologic and local immunologic alterations within the oral mucosa has led to a better understanding of these conditions and to the development of improved treatment strategies within the general practice setting for a significant number of otherwise healthy patients.