Ketamine is widely used in veterinary medicine. Its medical application in humans is limited to children because in adults it induces severe psychedelic episodes. In recent years, teenagers have abused ketamine as a recreational and "club drug" because of its hallucinogenic and stimulant effects. Ketamine is also misused as a "date-rape" drug (to induce amnesia in unsuspecting victims). Sensitive gas chromatography-mass spectrometry-negative chemical ionization (GC-MS-NCI) and liquid chromatography-mass spectrometry-atmospheric pressure chemical ionization (LC-MS-APCI) methods were applied for the simultaneous quantification of ketamine and its major metabolite, norketamine, in urine. Urine samples were collected from hospitalized children who had received ketamine as an anesthetic. Individual urine samples were collected up to 16 days after drug administration. Using the GC-MS-NCI method, ketamine was detected in the urine of the children from only the day of drug administration up to 2 days after drug administration. Its concentrations ranged from 29 to 1410 ng/mL. Norketamine (measured in concentrations of 0.1-1442 ng/mL) was detected up to 14 days. Using the LC-MS-APCI method, norketamine was detected up to 6 days after drug administration, ranging in concentrations of 2-1559 ng/mL, while ketamine was detected up to 11 days (2-1204 ng/mL). In the urine taken from one child, ketamine was not detected through the entire 16-day period using both methods. The detection window for the analytes is highly dependent on the method used for determination and varies between individuals.