A surgical classification of pediatric lumbosacral spondylolisthesis has been proposed recently. In this classification involving 8 distinct types of spondylolisthesis, the patient is classified according to: 1) the slip grade (low- vs. high-grade), 2) the degree of dysplasia (low- vs. high-dysplastic), and 3) the sagittal spinopelvic balance. The objective of this preliminary study is to assess the reliability of the classification. Two observers classified on two separate occasions 40 subjects with lumbosacral spondylolisthesis, based on standing postero-anterior and lateral radiographs of the spine and pelvis. No direct measurements on the radiographs were performed. All 8 types of spondylolisthesis were identified by the observers. Intra-observer agreement for the first and second observers was respectively 92.5% and 87.5%, while inter-observer agreement was 75.0%. Thirty-nine of 40 subjects had agreement among both observers according to the slip grade. Within these 39 subjects, observers disagreed for 8 subjects with respect to the degree of dysplasia and for only one subject with respect to the spinopelvic balance. The proposed classification could be used to better evaluate and compare available surgical techniques, and to develop a treatment algorithm for spondylolisthesis. This new classification results in good intra- and inter-observer agreement. Further studies with observers not involved in the design of the classification are however needed in order to confirm the relevance of the classification.