Scoliosis is a deformity of the spine that predominately atfects adolescent females. Mild scoliotic cwes are most vulnerable to progression during the adolescent powth spurt, however, only an unpredictable 15-25% progress to large incapacit at hg deformities. The present objective was to identify mechanical factors associated with the adolescent growth spurt which are instrumental to cwe progression in adolescent idiopathic scoliosis (AIS). An initially curveed and twisted, spatial beam-column model of a spine with a mild scoliosis was developed. The spine was embedded in a three-dimensional elastic medium to represent the ribcage. A finite element model of a ribcage was developed to establish its three-dimensional stiffness through a series of numerical experiments. Parametric analyses of both the ribcage and spine models were conducted to elucidate a better understanding of th mechanical systern. The geometry:​ material properties and applied loads of the spine were then systematicdy changed to simulate both nomal and aberrant growth patterns during the adolescent years. The three-dimensional stresses of the ribcage were found to vary significantly with rib level and orientation. and were most sensitive to changes in the gross ribcage geometry and the material properties of the costotransverse joints. The parametric analysis of the whole spine model indicated that the progression of a mild scoliosis was most sensitive to the initial Cobb angle. the spine length:​ the body weight and the lateral translational stifhess of the ribcage. The progression of a mild scoliotic curve (Cobb angle < 20°) was found to be smd due to mechanical changes associated with the normal adolescent growth spun in both males and females. For an initial Cobb angle of 30°, significant progression was predicted for a fernale during normal growth. The mechanical changes associated wlth reported aberrant growth pattern could be key factors in the progression of a mild scoliosis in a female, but not in a male. These results, which considered both the different geometry, stiffness and loads in growing females and males, strongly suggested a distinct difference in the progression tendencies between sexes, consistent with clinicai data. Although an aberrant growth pattern cannot fully explain curve progression in AIS. mechanical factors associated with the adolescent growth spurt should be considered to successfully predict the prognosis of a young scoliotic patient.