Objective:To introduce a method for posterior anlantoaxial fusion--Atlas lateral mass pedicle screw fixation for atlantoaxial instability.And to investigate the key point,indication and safety of this method.Method:From April 2005 to April 2006,7 cases suffered with atlantoaxial instability who were treated with atlas lateral mass pediclc screw fixation included 6 males and 1 females aged from 18 years old to 47 years (averaged 33 year old).Of these 4 cases suffered with acute traumatic atlantoaxial instability,3 cases suffered with old atlantoaxial instability,and spinal compression were found in 3 cases whose neurological symptoms disappeared after distraction for 1 to 3 weeks.