The purpose of this investigation was to document the degree of weakness present in the medial and lateral muscle groups of individuals with chronically unstable ankles. Peak isometric and isokinetic torque measurements were collected bilaterally during the motion of inversion-eversion from 33 subjects, ages 17 to 54, reporting unilateral chronic lateral instability. Values were then compared between the involved and uninvolved sides. A modified Romberg test was also performed bilaterally to determine gross balance differences between the involved and uninvolved lower extremities. No significant difference in muscle strength was documented either isometrically or isokinetically, but balance differences were found between the two extremities in a majority of subjects. The findings suggest that muscular weakness is not a major contributing factor to the chronically unstable ankle. The findings do support the presence of proprioceptive deficits associated with this condition. Based on the results, proprioceptive activities should be a primary consideration in management of the chronically unstable ankle. J Orthop Sports Phys Ther 1990;11(12):605-611.