We report a rare case of a 64-year-old female with metachronous secondary primary left occult breast cancer initially presenting right axillary lymph node metastases. The patient, who had received breast-conserving therapy for left breast cancer at another hospital about 4.5 years ago, came to our hospital complaining of right axillary node swelling. After both breast and systemic examination, she received complete right axillary lymph node dissection. Just after the operation, she was diagnosed with right occult breast cancer by a review of the right axillary lymph nodes and previous left breast cancer. She was followed by radiation and systemic chemoendocrine therapies. One year after axillary lymph node dissection, mammography and ultrasonography showed a new lesion in her left breast. Core needle biopsy revealed similar findings to right axillary lymph node metastasis. After salvage surgery, the diagnosis was revised. We recommend that patients without clinical findings except for axillary lymph node metastasis, especially post-breast-conserving surgery followed by radiation therapy, should be considered not only as having ipsilateral but also contralateral occult breast cancer. If there is no evidence of a primary lesion, axillary lymph node dissection needs to be carried out, and the patient should be offered the choice of radiation therapy or mastectomy followed by proper systemic therapy.