We describe two patients with multiple myeloma (MM) involving the central nervous system (CNS). In both patients, CNS involvement was manifested with extremely rare signs and symptoms. The first patient, a 64-year-old woman, developed obstructive hydrocephalus 10 years after the initial diagnosis of MM. The disease has been successfully treated with intrathecal chemotherapy, radiotherapy and systemic chemotherapy. The other patient, a 65-year-old man, developed hypopituitarism and diabetes insipidus 1 year after MM diagnosis. Disease in this patient proved resistant to both radiotherapy and chemotherapy; the patient died 2 years later. These rare complications add new information on the wide spectrum of clinical and laboratory manifestations of MM. It is obvious that descriptions of additional cases are required to better understand the mechanisms of CNS involvement in MM patients.