We describe a unique case of atypical natural killer (NK)-cell proliferation likely related to gluten sensitivity, mimicking NK-cell lymphoma. The patient, a 32-year-old man, has had persistent multiple erythematous bull-eye lesions in the stomach, small bowel, and large bowel for 3 years. Histologically, the lesions were well circumscribed and relatively superficial, composed of atypical medium-sized to large-sized lymphocytes with slightly irregular nuclear contours, a dispersed chromatin pattern, and clear cytoplasm. Immunohistochemistry and flow cytometry showed that the cells were NK cells expressing CD56 (aberrantly bright), T-cell intracellular antigen (TIA)-1, cytoplasmic CD3, and CD94, but not surface CD3, with bright aberrant expression of CD7 and a lack of other NK cell-associated markers. Polymerase chain reaction for rearrangement of the T-cell receptor-gamma chain gene showed no evidence of a clonal T-cell population, and in situ hybridization for Epstein-Barr virus encoded RNA was negative. There was no evidence of the involvement of peripheral blood or bone marrow. Although a diagnosis of extranodal NK/T-cell lymphoma was considered because of the atypical morphology and immunophenotypic aberrancy, no chemotherapy was given because of the relatively superficial nature of the infiltrates, lack of significant symptoms, and negativity for Epstein-Barr virus. Two years after initial presentation, the patient was found to have high titers of antigliadin antibodies with no other evidence of celiac disease. After instituting a gluten-free diet, many of the lesions regressed, suggesting that this atypical NK-cell proliferation may be driven by an anomalous immune response. Awareness of this case may prevent pathologists from misdiagnosing similar lesions as NK/T-cell lymphomas. It is as yet unknown whether this process occurs more commonly in patients with gluten sensitivity, or in other settings, and the pathogenesis is as yet undetermined.