We performed a prospective study of 302 patients who had a fracture of the lower extremity. Our purpose was to determine whether there was any association between impairment ratings of the lower extremity, derived with use of the Guides to the Evaluation of Permanent Impairment by the American Medical Association, and measurements of task performance based on direct observation as well as the patient's own assessment of activity limitation and disability as recorded on the Sickness Impact Profile.The mean residual impairment of the lower extremity according to the Guides was 27 per cent one year after the injury. Only 130 subjects (43 per cent) could perform all five functional tasks without difficulty. Eighty-four subjects (28 per cent) reported functional limitations that resulted in a score on the Sickness Impact Profile that was more than one standard deviation from the preinjury norm for the sample. Impairment ratings according to a modification of the system of the American Medical Association correlated strongly with the performance of functional tasks (r = 0.57) as well as the patients' reported activity limitations as recorded on the Sickness Impact Profile (r = 0.55). Correlations were highest when measures of impairment were based on strength rather than on range of motion. The relationship between the impairment rating and function (as observed by an examiner and as reported by the patient) was not influenced by the location of the fracture or the receipt of disability compensation.Our results suggest that the American Medical Association developed a valid approach for the measurement of physical impairment after a fracture of the lower extremity. In our study, the anatomical approach of evaluation based on muscle strength that was described in the Guides to the Evaluation of Permanent Impairment was the most sensitive measure of impairment compared with the anatomical measure based on range of motion and compared with the functional and diagnostic methods for the rating of impairment. Until the diagnostic and functional approaches for the measurement of musculoskeletal impairment are refined, we recommend use of the anatomical approach when evaluating impairment after a fracture of the lower extremity.