Carcinomatous meningitis is a rare complication of cancer with an unfavourable prognosis. In the population of patients diagnosed with breast cancer, it affects about 2–5% of patients. The clinical manifestation of symptoms is a consequence of the random deposition of neoplastic cells in different parts of the subarachnoid space. Multifocality of symptoms at one time is characteristic. A frequent cause of misdiagnosis is the performance of only a computed tomography scan of the brain, the image of which may remain normal. It should be remembered that the gold standard is magnetic resonance imaging with contrast. The paper presents a case of a 38-year-old female patient with the biological subtype of triple-negative breast cancer, who developed rapidly increasing neurological symptoms after recently completed oncological treatment. Their simultaneous and multifocal nature indicated damage to more than one level of the central nervous system. The aim of the study is to point out that the essence of the diagnosis of neoplastic meningitis is the awareness of the possibility of this complication in a cancer patient.