Lithium salts are widely used in treating psychiatric patients. Lithium may be associated with hyperparathyroidism, a risk factor for osteoporosis. However, the data on the effect of lithium on bone mass are conflicting. We assessed bone mineral density with dual-energy X-ray absorptiometry at the hip and lumbar spine in 75 lithium treated outpatients and 75 normal subjects matched for age, sex and body mass index. Serum total calcium, intact parathyroid hormone (PTH), estradiol, osteocalcin, total alkaline phosphatase (ALP) and C-telopeptide (CTX) in addition to fasting urinary calcium excretion were also determined in both groups. The mean (+/-SD) bone density in lithium treated patients was 4.5% higher at the spine (P<0.05), 5.3% higher at the femoral neck (P<0.05) and 7.5% higher at the trochanter (P<0.05). In addition, lithium treated patients had lower serum total ALP (P<0.005), lower serum osteocalcin (P<0.005) and lower serum CTX (P<0.05) but the total calcium, PTH and urinary calcium excretion did not differ significantly between patients and controls. In conclusion, our results suggest that maintenance therapy with lithium carbonate may preserve or enhance bone mass. These data also suggest a lower bone turnover state in those receiving lithium.