Twenty years ago, ketamine was introduced into clinical use in Germany. Since this time, advantages and disadvantages of "dissociative anesthesia" with ketamine have been reported in many studies. Improvements were seen in stabilization of blood pressure during induction of shock patients, induction of patients with asthma, and preservation of spontaneous breathing as well as protective reflexes. On the other hand, psychomimetic reactions and an increase in cardiac oxygen consumption restricted the clinical use of ketamine. The incidence of these side effects was reduced when ketamine was combined with benzodiazepines. In the course of time ketamine was used in obstetrics, as an analgesic agent, in burn patients, and in emergency and disaster medicine. The influence of ketamine on intracranial pressure and the endocrine stress response was investigated as well. Unconventional aspects were reported by several authors concerning oral, intrathecal, epidural, nasal, and rectal administration and the use of ketamine for intravenous regional anesthesia, whereby the local anesthetic properties of ketamine became evident. In conclusion, intravenous and intramuscular "sympathomimetic anesthesia" with ketamine has found its place in anesthesiology. Insufficient hypnotic properties can be diminished by combination with benzodiazepines. The main indications for ketamine are anesthesia and analgesia in emergency and disaster medicine. In clinical use, the substance is of benefit in the induction of anesthesia for cesarean section, in shock situations, for asthma patients, and for short operations and painful diagnostic procedures. Intramuscular administration is preferred in uncooperative patients and children. In intensive care medicine, ketamine is of special interest in patients with hypotensive circulatory dysregulation and in ventilator treatment of asthma patients.