Introduction: Adolescent idiopathic scoliosis (AIS) can affect spine mobility and gait mechanisms. Nowadays little is known about the effects of scoliosis on gait. Objectives: To evaluate the effects of untreated scoliosis on gait. Materials and Methods: Fifty-four females (13 healthy girls and 41 AIS with thoracolumbar/lumbar curve) were assessed by gait analysis. Xrays allowed classifying AIS patients into three groups, depending on the scoliosis severity. Gait analysis included synchronous bilateral kinematic and electromyographic (EMG) measurements, assessment of external (Wext), internal (Wint), total mechanical work (Wtot), oxygen consumption (V& O2), energy cost (C) and muscular efficiency (Wtot/C). Results: Shoulder, pelvis and hip motions were significantly reduced in all AIS patients. The reduced motion correlated with decreased Wtot. V& O2 and C were increased by 30 %. Muscle efficiency was decreased by 29 %. Increased C correlated with prolonged timing activity of lumbo-pelvic muscles (LPMTA). Discussion: Reduction of Wtot can be explained by decrease of external work. Increase of V& O2 and energy cost could be due to bilateral increase of LPMTA. Conclusion: Similar gait alterations were observed in all AIS patients, whatever the severity of the scoliosis. The observed alterations may be considered as the manifestation of an underlying neuromuscular disease or as a consequence of the stiffening effect of scoliosis. The observed “careful walking” strategy could also be a compensatory mechanism to minimize energy expenditure.