The effect of long-term use of depot medroxyprogesterone acetate (DMPA) on bone mineral density remains controversial. The present study compared bone mineral densities in 67 long-term (5 years or more) DMPA users recruited consecutively from the Hong Kong (China) Family Planning Association with those in 218 age-matched controls recruited from 8 family health service clinics in Hong Kong. Mean age was 42.8 years (range, 34-46 years) in the DMPA group and 40.0 years (range, 34-46 years) among controls. Body mass index, calcium intake, and smoking were similar in both groups. The median duration of DMPA use was 6 years (range, 5-15 years). Long-term DMPA users had significantly lower bone mineral densities than controls at the lumbar vertebra (0.93 vs. 1.03 g/sq. cm), neck of femur (0.69 vs. 0.83 g/sq. cm), trochanter (0.59 vs. 0.71 g/sq. cm), and Ward's triangle (0.58 vs. 0.78 g/sq. cm). The percentage of bone loss in L2-4 was more pronounced with increasing age. For each year of DMPA use, the decrease in bone mineral density was estimated to be 0.011 g/sq. cm (1.1%) in L2-4, 0.0193 g/sq. cm (2.3%) in the neck of femur, 0.0169 g/sq. cm (2.4%) in the trochanter, and 0.0277 g/sq. cm (3.5%) in Ward's triangle.