For perioperative anesthesia in a case of shoulder arthroscopy, a continuous interscalene plexus block according to Meier was performed in a 51-year-old female patient. The catheter was placed after stimulator-assisted punction and application of a local anesthetic. A few minutes after a further dose of local anesthetic was given via the catheter, the patient had to be intubated and ventilated with signs of total spinal anesthesia. The cervical CT showed the intrathecal displacement of the catheter, reaching the spinal canal near the root of the 7th spinal nerve. Blind advancement and deep placement increase the risk of an abnormal catheter position. Intraspinal misplacement should be reliably excluded.