Five cases of axillary lymphadenopathy are presented, which occurred after COVID-19 vaccination and mimicked metastasis in a vulnerable oncologic patient group. Initial radiologic diagnosis raised concerns for metastasis. However, further investigation revealed that patients received COVID-19 vaccinations in the ipsilateral arm prior to imaging. In two cases, lymph node biopsy results confirmed vaccination-related reactive lymphadenopathy. Ipsilateral axillary swelling or lymphadenopathy was reported based on symptoms and physical examination in COVID-19 vaccine trials. Knowledge of the potential for COVID-19 vaccine-related ipsilateral adenopathy is necessary to avoid unnecessary biopsy and change in therapy. © RSNA, 2021.