The aim of this study was to investigate the ability of a new hop test to determine functional deficits after anterior cruciate ligament (ACL) reconstruction. The test consists of a pre-exhaustion exercise protocol combined with a single-leg hop. Nineteen male patients with ACL reconstruction (mean time after operation 11 months) who exhibited normal single-leg hop symmetry values (> or =90% compared with the non-involved extremity) were tested for one-repetition maximum (1 RM) strength of a knee-extension exercise. The patients then performed single-leg hops following a standardised pre-exhaustion exercise protocol, which consisted of unilateral weight machine knee-extensions until failure at 50% of 1 RM. Although no patients displayed abnormal hop symmetry when non-fatigued, 68% of the patients showed abnormal hop symmetry for the fatigued test condition. Sixty-three per cent exhibited 1 RM strength scores of below 90% of the non-involved leg. Eighty-four percent of the patients exhibited abnormal symmetry in at least one of the tests. Our findings indicate that patients are not fully rehabilitated 11 months after ACL reconstruction. It is concluded that the pre-exhaustion exercise protocol, combined with the single-leg hop test, improved testing sensitivity when evaluating lower-extremity function after ACL reconstruction. For a more comprehensive evaluation of lower-extremity function after ACL reconstruction, it is therefore suggested that functional testing should be performed both under non-fatigued and fatigued test conditions.