SummaryThe trick or supplementary movements which have been observed in 170 cases of peripheral nerve injuries have been described. These are voluntary movements which can still be effectively carried out even when those muscles customarily held to be responsible for their execution have been deprived of their nerve supply.Trick movements have been recorded in isolated and combined lesions of all the main peripheral nerves.The immediate recognition of such movements in peripheral nerve injuries is of considerable importance since the failure to detect them will lead to false estimates of the extent of the nerve lesion and the progress of regeneration. This will in turn result in incorrect diagnoses and in unjustified optimism concerning either the progress of spontaneous regeneration or the efficacy of a surgical procedure designed and undertaken to facilitate regeneration.Attention has been directed to the care which must be exercised in testing voluntary movements and in estimating, solely on the basis of the derangement of movement, the condition of any muscle or muscles.