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Case series and a biomechanical study using a finite element (FE) analysis.To report three cases with multi-level spondylolysis and to understand the mechanism biomechanically.Multi-level spondylolysis is a very rare condition. There have been few reports in the literature on multi-level spondylolysis among sports players.We reviewed three cases of the condition, clinically. These patients were very active young sports players and had newly developed fresh L4 spondylolysis and pre-existing L5 terminal stage spondylolysis. Thus, we assumed that L5 spondylolysis may have increased the pars stress at the cranial adjacent levels, leading to newly developed spondylolysis at these levels. Biomechanically, we investigated pars stress at L4 with or without spondylolysis at L5 using the finite element technique.L4 pars stress decreased in the presence of L5 spondylolysis, which does not support our first hypothesis.It seems that multi-level spondylolysis may occur due to genetic and not biomechanical reasons.