Oral non-Hodgkin lymphomas are uncommon, and those arising on the gingiva are rare. A case of non-Hodgkin lymphoma of the gingiva that was erroneously diagnosed and treated as a dental abscess is presented. Clinical examination showed a firm and ulcerated mass extending from the mandibular right first premolar region to the retromolar trigone. Resorption of the alveolar ridge was radiographically observed. Histologic analysis revealed a large B-cell non-Hodgkin lymphoma. No other evidence of the disease was found except in the mandible. The patient was treated with chemotherapy that resulted in complete regression. As primary non-Hodgkin lymphoma of the gingiva can be misdiagnosed as a trivial inflammatory lesion, a histologic examination should be mandatory in those cases in which symptoms do not subside after specific treatment.