An adult male skeleton from the early Neolithic cemetery of Shamanka II on the south coast of Lake Baikal (Siberia, Russia) presents one of most striking examples of upper limb bilateral asymmetry documented without obvious indicators of skeletal pathology or trauma to the afflicted arm. The condition is noteworthy not only for its severity, with asymmetry values as high as 89.5%, but also for its involvement of the whole upper extremity, from clavicle to manual phalanges. The lack of any demonstrable hypertrophy on the unaffected left arm, and the clear evidence of extensive hypotrophy/atrophy on the right, leave little doubt that this asymmetry has a pathological or traumatic basis rather than a functional (activity-induced) one. It most likely reflects paralysis or paresis of the entire right arm resulting from complete brachial palsy incurred prior to the attainment of skeletal maturity in that limb.