Iidaka T, Muraki S, Oka H, et al. - Using a large-scale population of a nationwide cohort study, Research on Osteoarthritis/osteoporosis Against Disability (ROAD), researchers studied the incidence and progression rate of radiographic hip osteoarthritis (OA) and its risk factors in Japanese men and women. Two thousand nine hundred seventy-five candidates aged 23 to 94 years (mean, 70.2 years) living in urban, mountainous, and coastal communities were followed up with hip radiography at 3, 7, and 10 years from the baseline survey of the ROAD study. In men and women, respectively, the radiographic hip OA incidence rate was 5.6/1,000 person-years and 8.4/1,000 person-years. In men and women, respectively, hip OA progression rate was 2.2/1,000 person-years and 6.0/1,000 person-years. Age, obesity, and acetabular dysplasia at baseline were the significant risk factors for incident hip OA. Baseline hip pain and acetabular dysplasia were the significant risk factors for progressive hip OA. Continued longitudinal ROAD study surveys will contribute to knowledge and potential incident prevention and progressive hip OA.