A 30-year-old woman was pointed out for her right axillary lymphadenopathy in a medical checkup. Ultrasonography showed two swollen lymph nodes and the presence of lymph node hilum with a convex shape in the larger lymph node. Under the tentative diagnosis of lymphadenitis, the patient was initially treated with antibiotic therapy, leading to no improvement in her lymphadenopathy for 1 month. Positron emission tomography after antibiotic therapy showed a maximum standardized uptake value of 7.0 in the swollen lymph nodes without any other avidities. Neither mammography nor ultrasonography showed any abnormalities in the breasts. The serum IL-2R level was within the normal range. Despite the lack of malignant cells in the aspiration biopsy cytology specimen, the patient received lymph node excisional biopsy to avoid undertreatment. A postoperative pathological study showed a swollen lymph node with preserved lymph node structure, follicular hyperplasia, and lymphoid hyperplasia. The irregularly dilated germinal center had microglanulomas, tingible body macrophages, enlarged aggregation of monocytoid B cells with neutrophil interminglement, and no giant cells, leading to the diagnosis of toxoplasmosis. A detailed interview after the lymph node biopsy revealed that she did not have any cats but had chickens and had her right forearm a little injured by the roof edge of a chicken coop 5 weeks before the medical checkup. Postoperative serologic testing to further confirm the toxoplasma infection showed elevated IgG and IgM antibody levels. Oncologists and infectious disease specialists should note this type of transmission of toxoplasma gondii and unilateral lymphadenopathy as an important clinical manifestation of toxoplasmosis.