This is a prospective randomized study to compare the outcome of two widely used fusion methods ; posterior lumbar interbody fusion (PLIF) and posterolateral fusion (PLF) in treatment of adult low grade lytic spondylolisthesis to know which is ideal. 40 consecutive patients with single level lytic spondylolisthesis were randomly divided into two treatment groups when undergoing surgery. Blood loss and operative time were recorded. Patients were postoperatively assessed using JOA score. Union rate was assessed. They were followed up for a minimum of 2 years. No differences were found between both groups as regards operative time and blood loss. At 2 years follow up, statistically significant improvement in JOA scores were found in both fusion groups. However, no difference could be found between the groups. Both groups showed solid fusion with no evidence of non-union in all cases. Both methods appear to be equally effective in treatment of the condition.