Sickle cell disease (SCD) is a prevalent genetic disorder in which sickle hemoglobin leads to tissue hypoxia and adverse effects on bone. Published studies suggest that children with SCD often have undiagnosed osteopenia or osteoporosis. Minimal data exist on the prevalence of low bone mineral density (BMD) in adults. Our objective was to describe the prevalence of osteopenia and osteoporosis in adults with SCD and to identify patient or disease characteristics associated with low BMD. We conducted a cross-sectional study of adults with SCD. Through questionnaires, we collected data about disease course and osteoporosis risk factors. Patients underwent dual X-ray absorptiometry (DXA) measurement of BMD at the hip, spine, and forearm and sampling of blood and urine for markers of bone turnover, sickle cell disease severity, and secondary causes of osteoporosis. Our main outcome measure was prevalence of osteopenia and osteoporosis as defined by WHO criteria. Of 32 adults with SCD (14 men and 18 women) with a mean age of 34 years, 72% (95% confidence interval 53–86%) had low BMD at one or more anatomic sites. Thirteen patients were classified as osteoporotic and 10 as osteopenic. The prevalence of low BMD was greatest in the lumbar spine (66% of patients). Significant correlates of decreased BMD included low BMI (P < 0.01), male sex (P = 0.02), and low serum zinc concentrations (P < 0.01). The prevalence of osteopenia and osteoporosis in young adults with SCD is extremely high. Further research is needed to address fracture risk and therapeutic interventions. Am. J. Hematol. 81:236–241, 2006. © 2006 Wiley-Liss, Inc.