In order to increase the knowledge of locomotor disturbances in children with autism, and of the mechanism underlying them, the objective of this exploratory study was to reliably and quantitatively evaluate linear gait parameters (spatio-temporal and kinematic parameters), upper body kinematic parameters, walk orientation and smoothness using an automatic motion analyser (ELITE systems) in drug naive children with Autistic Disorder (AD) and healthy controls. The children with AD showed a stiffer gait in which the usual fluidity of walking was lost, trunk postural abnormalities, highly significant difficulties to maintain a straight line and a marked loss of smoothness (increase of jerk index), compared to the healthy controls. As a whole, these data suggest a complex motor dysfunction involving both the cortical and the subcortical area or, maybe, a possible deficit in the integration of sensory-motor information within motor networks (i.e., anomalous connections within the fronto-cerebello-thalamo-frontal network). Although the underlying neural structures involved remain to be better defined, these data may contribute to highlighting the central role of motor impairment in autism and suggest the usefulness of taking into account motor difficulties when developing new diagnostic and rehabilitation programs. (Contains 4 tables and 2 figures.)