Lamotrigine, as a new generation anticonvulsant and mood stabilizer, has been widely used in treating epilepsy and bipolar disorder. However, the Japanese Ministry of Health, Labour and Welfare has warned of the adverse reaction of lamotrigine. We here report a case of severe stomatitis associated with lamotrigine. A 64-year-old man presented with severe stomatitis without skin rash. He had been taking lamotrigine for bipolar disorder for at least 18 months. We suspected this adverse reaction to be due to lamotrigine. Soon after lamotrigine was stopped by the attending psychiatrist, the symptoms of stomatitis completely resolved. We finally diagnosed severe stomatitis induced by lamotrigine based on his past and recent experience. Oral surgeons should be aware of the possibility of severe stomatitis caused by lamotrigine.