 Blockage of the transverse abdomen TAP promotes excellent analgesia of the abdominal wall and the parietal peritoneum. The meta-analyzes in adults demonstrate improved of postoperative pain and analgesic s consumption. There are few studies on TAP block in open appendectomies and laparoscopic in pediatrics, they show good results. There is a consensus of the best anesthetic volume for good infiltration of the TAP block, but there are still doubts in the literature about the best concentration of local anesthetics of long duration. The main objective of this prospective, randomly distributed and double-blind clinical trial is to evaluate two concentrations of 0.25 and 0.5 ropivacaine with a volume of 0.4 ml kg in pain control and the analgesic consumption through 24 hours observation in open Appendectomy in children between 6 and 16 years. 3 groups were being compared: the control group has received no blockade, the other two groups have received TAP blocks if ropivacaine 0,25 and 0,5 0.4mlkg. All pacients patients received the same protocols anesthesia and analgesia. The provided analgesia was dipyrone every 6 hours and ketoprofen every 8 hours, and rescue analgesia was tramadol every 4hours if it were required. The FACE pain scale was used to evaluate the postoperative pain. 