OBJECTIVE:To evaluate reliability, validity and responsiveness of HOOS-12, a 12-item short form of the 40-item Hip disability and Osteoarthritis Outcome Score (HOOS). HOOS-12 provides Pain, Function and Quality of Life (QOL) scale scores and a summary hip impact score. DESIGN:Data from 1,273 FORCE-TJR hip osteoarthritis (OA) patients who completed HOOS before and six and 12 months after total hip replacement (THR) were analyzed. HOOS-12 includes a pain frequency item and three items measuring pain during increasingly difficult (sitting/lying, walking, stairs) activities; function items about standing, rising from sitting, getting in/out of a car, and walking on an uneven surface; and the 4-item HOOS QOL scale. Percent computable scale scores, floor and ceiling effects, internal consistency reliability, validity (scale correlations, tests of known groups validity using one-way analysis of variance (ANOVA)), and responsiveness (effect sizes (ES), standardized response means (SRM)) were compared for HOOS-12, full-length HOOS, HOOS-PS and HOOS, JR. RESULTS:Internal consistency reliability was above 0.70 for all HOOS-12 scales and above 0.90 for the HOOS-12 Summary score. Validity and responsiveness of HOOS-12 Pain, Function and QOL scales were satisfactory and reached similar conclusions as comparable full-length HOOS scales. The HOOS-12 Summary score was highly responsive in discriminating between groups who differed in global ratings of post-THR change in physical capabilities and had high ES and SRM standardized response means. CONCLUSIONS:HOOS-12 was a reliable and valid alternative to HOOS in THR patients with moderate to severe OA and provided three domain-specific and summary hip impact scores with substantially reduced respondent burden.