PURPOSE: (1) To describe ankle strength and postural stability in patients with chronic lateral ankle instability and (2) to analyse the correlation between deficits in ankle strength and postural stability. METHODS: Results of preoperative isokinetic and balance tests in 203 patients whose contralateral ankle was normal were retrospectively reviewed. Isokinetic peak torque values of eversion and inversion at 2 angular velocities (30°/s and 120°/s) were measured in the injured and normal ankles. In the balance test, the percent differences of 3 actual scores (overall, anterior-posterior, and medial-lateral) between the injured and normal ankles were calculated. Additional statistical analyses were performed to evaluate weakness of ankle strength, postural stability deficits, and their correlation. RESULTS: Significant differences in 4 peak torque values and 4 relative peak torque values (peak torque/body weight) were found between the injured and normal ankles. All 8 values were significantly lower in the injured ankles. Weakness was severe during inversion and at 30°/s. In the balance test, 49 subjects (24.1%) had significant deficits in postural stability and 109 (53.7%) had favourable results. No strong association was found between weakness of ankle strength and deficits in postural stability. CONCLUSIONS: Strength measurement alone is insufficient to evaluate preoperative functional deficits, and other functional tests are required to measure postural stability. The results of this study provide further evidence for a rehabilitation programme consisting of proprioceptive training as well as strengthening. The proprioceptive training must be an integral part of the rehabilitation programme in addition to strengthening exercise. LEVEL OF EVIDENCE: Case series, Level IV.