Osteopenia at the hip and low total body calcium content have been reported in women with Marfan syndrome. Using dual X-ray absorptiometry (DXA), we evaluated the lumbar spine L2-L4 and proximal femur bone mineral density (BMD,/cm2) in 32 women and 16 children with Marfan syndrome. The women were 38 +/- 10 (SD) years old (23-58 years); their mean height was 178.7 +/- 8 cm. The children (9 boys and girls were 9.9-17.5 years old. Children were tall for their ages but of normal weight. All subjects were moderately active, without previous nontraumatic fracture. In the women, BMD was reduced at L2-L4, femoral neck (fnk), trochanter (tr), and intertrochanter (intr) (p < 0.0001-0.006), compared with age-predicted values. Z scores for L2-L4 and for the fnk, tr, and intr, were -0.59 +/- 1.06,-1.25 +/- 0.99,-1.03 +/- 0.91, respectively. The average hip axis length (HAL) of 11.5 +/- 0.093 cm was at the 80th percentile for women. No significant change was observed in 1 year follow-up BMD measurements in 13 women (fnk = -0.23 +/- 2.3%/year; L2-L4 = -0.43 +/- 1.57%/year). In Marfan children, BMD correlated with age, height, and pubertal development. Femoral neck BMG was reduced (Z = -0.74 +/- 1.22,p < 0.05) with a nonsignificant trend toward decreased BMD at L2-L4 (Z = 33 +/- 1.48). Resorption markers in Marfan women were normal and did not correlate with bone status. We conclude that women with Marfan syndrome have both axial and peripheral osteopenia as well as an increased HAL. This combination of findings likely increases substantially their long-term risk for hip fracture. Presence of osteopenia in Marfan children indicates that the skeletal deficits of Marfan syndrome may reflect inadequate bone acquisition.