Malignant lymphoma may occur in the oral cavity and oropharynx, but is most commonly located in Waldeyer's ring, particularly in the palatine and lingual tonsil. Non-Hodgkin's lymphoma mimicking feature of pericoronitis is a rare entity. Clinical features are nonspecific ulcerative lesions that do not heal. In the literature, the majority of cases are non-Hodgkin's lymphoma, diffuse large B cell type; however T-cell phenotype also may occur. We describe a 45-year-old woman who presented with an operculits in the left lower 3rd molar region, unresponsive to local antiseptic mouthrinses, antibiotics and other drugs and procedures for pericoronitis. After tissue biopsy, histopathological and immunohistochemical analyses confirmed a diagnosis of non-Hodgkin's lymphoma, B cell type.