Objectives: To study clinical and paraclinical characteristics shown in 52 patients allergic to Carbamazepine and Allopurinol, which supposedly lead to the syndrome of Steitens-Johnson and Lyell (SIS & TEN), at Center of Allergology and clinical immunology, Bach Mai hospital, during the period of January 2012 to June 2013, study describes the process of retrospective in association with randomized. the study indicates that male patients account for 61.5 percent, which is more 38.5 percent of female patients, where the average age of the patients is 45.6 + or - 19.5. The average age of the patients suffering from the carbamazepine allergy is 37.3 + or - 16.8, which is inferior to the average age (58.9 + or - 16.0) of the patients having allopurinol allergy. The average days under treatment of the patients associated with carbamazepine allergy is (11.3 + or - 4,2 days), which is less than that value (14.5 + or - 8.6 days) of the patients suffering from allopurinol allergy. The carbamazepineallergy patients have the SCORTEN index of (0,6 + or - 0,9 points), which is lower than the SCORTEN index (1.4 + or - 1.1 points) of the allopurinol - allergy patients.