Because the peroneal muscles are thought to act as a safeguard against lateral ankle injury, it is important to study their function. This study was undertaken to electromyographically assess the latency between sudden unexpected ankle inversion and the start of peroneal muscle activity. Three groups participated in the study, including subjects with lateral ankle sprain rehabilitated nonsurgically (N = 7), sprains rehabilitated following surgery (N = 6), and injury-free ankles (N = 11). Peroneal latency was assessed by dropping the subjects into inversion from a special platform. The platform was designed so that either ankle could be inverted to 35 degrees without warning. The ANOVA revealed no significant latency differences (p > .05) between the three groups. The study suggests that bilateral peroneal latency is unaffected by injury. Although it has been thought that healthy muscles provide a defense against ankle sprain, their latency is not permanently affected by ankle injury or by surgery performed to correct defects from injury. It appears that mechanoreceptor impairment may be rehabilitated and that it is not a factor in ankle injury.