A 52-year-old woman came to the emergency department with seizures and right lower quadrantopsia. Her medical history was notable for a clinical stage IV pure HER2 right breast adenocarcinoma due to liver involvement, which was diagnosed approximately 2 years earlier. She underwent chemotherapy treatment, right radical mastectomy, continuing with immunotherapy until presenting the neurological event. Imaging studies revealed a left parietal occipital mass with a meningeal base. She underwent a study of the cerebrospinal fluid being negative for neoplastic cells and infection, and a biopsy of the meningeal lesion, resulting in metastatic breast adenocarcinoma. Together with the results, a single leptomeningeal metastasis was diagnosed. This clinical case presents a rare complication for the pure HER2 subtype, but known from breast cancer with long survival.