Posterior lumbar interbody fusion (PUF) is now considered to be the golden standardJor lumbar instability caused by spondylolysis or spondylolisthesis. PLIF has many limitations because oj the technical difficuLties, complications and the gained postoperative increase oj the disc height tends to retum to preoperative level. The use ojpoly-ether-ether ketone cageJor posterior lumbar interbody Jusion is technically less difficult with minimal complications. Twelve patients; ten were Jemale and two male; with spondylolysis and spondylolisthesis oj diJferent causes were treated by PEEK interbody cage and interpedicularfixation with or without posterolateral Jusion. Age oj the patients rangedJrom 38 to 62 years (mean 50 years). The patients were Jollowed Jor a mean 1 year duration and were evaluated both clinically and radiologically. All twelve patients were improved clinically except two patients had partial improvement with occasional and temporary back pain due to causes other than cage complications.