One widely held theory on the pathogenesis of adolescent late-onset tibia vara is that obesity coupled with mild preexisting varus alignment produces forces sufficient to retard growth in the medial portion of the proximal tibial physis and initiates the development of the condition. Two cases are presented in which neutral mechanical alignment was clearly documented in an extremity that subsequently developed adolescent late-onset tibia vara within 19 months. We conclude that in at least some cases, preexisting varus alignment is not a prerequisite for the development of adolescent late-onset tibia vara.