Bone mineral density (BMD) is a significant determinant of risk for osteoporosis. Genetic factors are known to account for a major proportion of variation of BMD in Caucasians. However, the degree of genetic determination of BMD in Chinese populations has seldom been investigated. The aim of our study was to investigate the magnitude of the genetic determination of BMD at the spine and hip, and their genetic covariation, in a population of Shanghai city in P. R. China. The subjects consisted of 44 full-sib pairs of females aged 19-43 years, 186 mother-daughter pairs, and 270 nuclear families. For BMD at the spine and hip, the values for narrow-sense heritability h2 (+/-SE) were 0.72+/-0.14 and 0.87+/-0.14, respectively, when estimated by full-sib pairs, and 0.44+/-0.07 and 0.77+/-0.07, respectively, when estimated by mother-daughter pairs. There was a significant genetic correlation r(g) (+/-SE) of BMD between the spine and hip, of 0.97+/-0.01 and 0.76+/-0.04, respectively, when estimated by full-sib pairs and mother-daughter pairs. The common household impact on BMD in our study was negligible according to the statistical estimate. We conclude that genetic factors play a major role in the determination of the variation and covariation of BMD at the spine and hip in our Chinese sample.