Recent studies indicate that decreased bone mineral density (BMD) occurs in the spine, femoral necks and greater trochanters of some adults and children with Marfan syndrome. Because there is uncertainty regarding the BMD status of patients with Marfan syndrome, we undertook an analysis of BMD in both adults and children with Marfan syndrome. Dual energy X-ray absorptiometry analysis was performed on a convenience sample of 51 patients (30 adults and 21 children) with diagnosed Marfan syndrome from 1993 to 2000. T-Scores (i.e. the number of standard deviations above or below the average normal peak bone density) were determined for comparison of adults. Mean±SD of individual BMD values were used for comparison of the data of children. Compared to standard values obtained from normal adult patients, adult males with Marfan syndrome demonstrated significantly reduced femoral neck BMD with an average T-score of -1.54 (P<0.001), diagnostic of osteopenia. Although osteopenia and osteoporosis were observed in several middle aged and pre- and postmenopausal women, the average T-score value for adult females and children were within normal limits. The etiology and full significance of decreased BMD in adult male patients with Marfan syndrome remain uncertain at the present time. Our results lead us to question the value of aggressive BMD evaluations by DXA in these patients, particularly prior to reaching mid-age. Further investigations will be required to shed insights into the natural history of BMD in adults and children with Marfan syndrome. Any application of bone mineral replacement therapy such as bisphosphonate, selective estrogen receptor modulators, hormone replacement therapy and vitamin D in these patients may be premature based on the existing evidence.