A discoid lateral meniscus in the knee is more common in Asian populations. The aim of this study was to evaluate the influence of arthroscopic meniscectomy of the discoid lateral meniscus on the axial alignment of the lower limb in adolescents (younger than twenty years of age).We retrospectively reviewed the data from 298 adolescent patients (younger than twenty years of age) who underwent arthroscopic treatment in our center from 2004 to 2013. Patients were divided into three groups according to the meniscus type: torn discoid lateral meniscus (Group A), torn nondiscoid lateral meniscus (Group B), and nondiscoid lateral meniscus without a tear (Group C). The tibiofemoral angle (TFA) and mechanical axis deviation (MAD) of both lower limbs were examined on standing anteroposterior radiographs before and after arthroscopy.The preoperative TFA and MAD of the ipsilateral lower limbs demonstrated significantly more varus in Group A than in Group B (p 0.01), after we controlled for the contralateral lower limb as the covariate factor. Additionally, the reductions in the TFA and MAD (varus inclination) in Group A were significantly greater than those observed in Group B (p < 0.001).The axial alignment of the lower limb in adolescents (younger than twenty years of age) with a torn discoid lateral meniscus was altered immediately after arthroscopic meniscectomy: the varus deformity was significantly reduced, and a valgus inclination developed in some of these patients. The valgus inclination was more pronounced in the patients with a torn discoid lateral meniscus compared with those with a torn nondiscoid lateral meniscus.