The inverse relationship between osteoporosis and osteoarthritis (OA) was first noticed 20 years ago. The subject, however, remains controversial. Recent observations on bone mineral density (BMD) in large epidemiological population surveys confirmed that cases with generalized OA had significantly increased bone mass at the axial and peripheral skeleton compared to age and sex matched controls corrected for body weight. Because OA cases have significantly increased bone width, BMD at the forearm is not significantly increased in some studies. The association of moderate to severe OA with increased appendicular and axial BMD is comparable to that of other determinants of bone mass, including 10 years of age and 10 kg of body weight, and thus may confer protection against fracture, especially of hip fracture.