Appropriate muscular response following an external perturbation is essential inpreventing falls. Transtibial prosthesis users lack a foot-ankle complex and associatedsensorimotor structures on the side with a prosthesis. Its effect on rapid responses ofthe lower-extremity to external surface perturbations is unknown. The aim of thepresent study was to compare electromyographic (EMG) response latencies of otherwisehealthy unilateral transtibial prosthesis users (n=23, mean age 48 years [standarddeviation 14]) and a matched control group (n=23, mean age 48 years [standard deviation13]) following sudden support surface rotations in the pitch plane (toes-up and toesdown).Perturbations were elicited in various weight-bearing and limb-perturbedconditions. The results indicated that transtibial prosthesis users have delayed responsesof multiple muscles of the lower-extremity following perturbation, both in the intact limband the residual limb. Weight-bearing had no influence on the response latency in theresidual limb, but did on the intact limb. Which limb received the perturbation wasfound to influence the muscular response, with the intact limb showing a significantlydelayed response when the perturbation was received only on the side with a prosthesis.These delayed responses may represent an increased risk of falling for individuals thatuse a transtibial prosthesis.