Pelvic radiographs of 200 consecutive Japanese Oriental patients who were admitted for hip surgery at the Hospital of Kobe University in Japan were compared with those of 199 consecutive American white patients who were admitted for the same purpose to a New England hospital over a similar four and a half-year period between 1972 and 1976. One hundred and fifty-three Japanese Oriental and 157 American white patients had either primary or secondary osteoarthritis. The remainder had other types of hip pathology, such as avascular necrosis, rheumatoid arthritis, and ankylosing spondylitis. The radiographs of five Japanese Oriental and seven American white patients showed evidence of previous Legg-Calvé-Perthes disease, coxa vara, or slipped capital femoral epiphysis. With only two exceptions, the osteoarthritis in the remainder of the Japanese Oriental patients was secondary, caused by antecedent congenital hip disease: twenty-eight had one or two congenitally dislocated hips, ninety-two had acetabular dysplasia, and twenty-six had superolateral osteoarthritis. In contrast, only nine of the American white patients clearly had a diagnosis of acetabular dysplasia, and twenty-six had superolateral osteoarthritis. Twenty-one American white men had a femoral head-tilt deformity. Among the Americans, the largest group (sixty-five patients) had superomedial osteoarthritis. Nine had non-rheumatoid protrusio acetabuli and twenty had axillary or concentric osteoarthritic involvement. The majority of American white patients, therefore, had a type of osteoarthritis that was not seen in the Japanese Oriental patients.(ABSTRACT TRUNCATED AT 250 WORDS)