['To evaluate the validity, reliability, responsiveness, and mode preference of electronic data capture (EDC) using the Western Ontario and McMaster (WOMAC) numerical rating scale (NRS) 3.1 Osteoarthritis (OA) Index on Motorola V3 mobile phones.', 'Patients with OA undergoing hip or knee joint replacement were assessed preoperatively and 3-4 months postoperatively, completing the WOMAC Index in paper (p-WOMAC) and electronic (m-WOMAC) format in random order.', 'Data were successfully and securely transmitted from patients in Australia to a server in the United States. Pearson correlations between the summated total index scores (TISs) for the p-WOMAC and m-WOMAC pre- and postsurgery were 0.98 and 0.99 (P<0.0001). There were no clinically important or statistically significant between-method differences in the adjusted total summated scores, pre- and postsurgery (adjusted mean differences=4.44, P=0.474 and 1.73, P=0.781, respectively). Internal consistency estimates of m-WOMAC reliability were 0.87-0.98. The m-WOMAC detected clinically important, statistically significant (P<0.0001) improvements in pain, stiffness, function, and TIS. No statistically significant differences in mode preference were detected.'] Is osteoarthritis Index delivered by mobile phone ( m-WOMAC ) valid , reliable , and responsive?