<p><b>OBJECTIVE</b>To explore the association between the leg length discrepancy and postoperative function after total hip arthroplasty.</p><p><b>METHODS</b>From June 2004 to June 2007, the Leg length in 80 consecutive patients (38 males and 42 females, ranging in age from 56 to 86 years, with an average of 72.3 years) who underwent primary unilateral total hip arthroplasty was measured radiologically. Postoperative hip function and patients' satisfaction was assessed using the Oxford Hip Score (OHS) at three months and one year after surgery.</p><p><b>RESULTS</b>(1) Leg length: 52 operated legs were longer than the other side by a mean of (9.2+/-3.2) mm (1 to 22 mm), in which 29 legs were longer for 1 to 10 mm (mean value 4.9 mm) and 23 legs were longer for 11 to 22 mm (mean value 14.6 mm); 13 operated legs were shorter by a mean of (6.4+/-2.1) mm (3 to 19 mm); 15 operated legs were of the same length as the other side. (2) Oxford hip scores: At three months after operation, the mean Oxford hip scores in patients with lengthened legs (two groups) were significantly higher (i.e., worse) than in the patients with shortened legs or in patients with legs of the same length. Significant difference in Oxford Hip Score was not found between the two groups of lengthened legs (1 to 10 mm vs 11 to 22 mm). Significant difference in Oxford Hip Score was also not found between the patients with shortened leg and the patients with legs of the same length. At one year after operation, the Oxford hip scores were significantly higher (i.e. worse) in the patients with lengthened limbs (11 to 22 mm) than in those of shortened limbs, or with limbs of equal length, or patients with lengthened legs (1 to 10 mm). No significantly differences of the Oxford hip scores were found within the patients with shortened limbs, the patients with limbs of equal length and the patients of lengthened limbs (1 to 10 mm). There was no significant difference between the Oxford hip scores at three months' follow-up and that at one year's follow-up in the lengthened group (11 to 22 mm), shortened group or same length group. The Oxford hip score was improved significantly one year after surgery when compared with that of three months after surgery in the lengthened group (1 to 10 mm).</p><p><b>CONCLUSION</b>Leg length discrepancy, especially for that 11 to 20 mm longer than the healthy side, affects the functional outcome after total hip arthroplasty, and it does not relieve over time. Well planned measures should be taken to minimize leg length discrepancy.</p>