Background: Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is known as a rare adverse event with chemotherapy. We report the case of a SIADH occurring after vinorelbine treatment. Case Report: In a 79-year-old woman breast cancer was first diagnosed in 2000. Three years after the first diagnosis the patient developed bone and liver metastases. Seven days after receiving the 1st course of palliative chemotherapy with vinorelbine the patient suffered from decreased mental awareness, fatigue, and physical weakness. After the diagnosis of SIADH based on laboratory findings in combination with clinical symptoms, we started therapy with balanced fluid intake and intravenous infusion of normotonic saline. Conclusion: The development of SIADH as a rare adverse event with vinorelbine treatment has to be taken into consideration.