Risk of knee osteoarthritis (OA) associated with constitutional factors, history of joint injuries, and occupational factors was assessed in a case-control study among women in Japan. Results were contrasted with a comparable study in Britain. The study covered 3 health districts in Japan. Cases were women aged >/= 45 years old, diagnosed with knee OA by orthopedic physicians utilizing radiography. No cases displayed established causes of secondary OA. Controls selected randomly from the general population were individually matched to each case for age, sex, and residential district. Subjects were interviewed using structured questionnaires to determine medical history, including history of joint injury, physical activity, socioeconomic factors, and occupation. Height and weight were measured. Interviews were obtained from 101 female cases and controls. The highest third of heaviest body weight in the past [high (> 62.0 kg) vs low (< 55 kg) odds ratio = 4.42, 95% confidence interval 1.17-16.64], previous injury to the knee (OR 7.11, 95% CI 2.40-21.09), sedentary work during initial employment (OR 0.35, 95% CI 0.15-0.84), and total working years (OR 1.05, 95% CI 1.01-1.08) represented independent factors associated with knee OA, after controlling for other potential risk factors. Heavy weight in the past appears to represent a risk factor for knee OA among women in Japan, as reported in Britain. Constitutional factors may represent important determinants for knee OA, regardless of race. Previous injury to the knee and occupational factors are also associated with knee OA in both Britain and Japan, although characteristic activities for work vary.