It is generally believed that bone mineral density (BMD) is increased in obese subjects, but the effect of weight loss on BMD has not been well studied. Therefore, we evaluated BMD among 11 obese women (mean age 45.5 +/- 14.2 years) before and after weight loss achieved by ingesting an 800 calorie diet for 12 weeks. BMD measurements were made at baseline, 6 months and 1 year intervals. Urinary hydroxyproline:creatinine (H:Cr), calcium:creatinine (Ca:Cr) ratios were measured as indices of bone turnover. Mean weight at baseline was 103.8 +/- 15.8 kg and decreased to 83.2 +/- 12.2 at six months and was 85.8 +/- 14.2 kg at one year. Total body, hip and lumbar spine BMD were 1.12 +/- 0.07, .87 +/- 0.11, and 1.02 +/- 0.12 gm/cm2, respectively. Total body BMD was significantly lower at 12 months compared to baseline. No significant change was observed in BMD of the lumbar spine. There was also a significant decrease in hip BMD at six months and 12 months compared to baseline. H:Cr and Ca:Cr ratios did not change over time. We conclude that weight loss achieved by VLCD is accompanied by a statistically significant change in BMD, but the BMD remained in the normal range.