To examine the prevalence of and risk factors for low bone mineral density (BMD) and vertebral fractures in patients with systemic lupus erythematosus (SLE). We studied 107 SLE patients. Demographic and clinical data were collected, and radiographs of the thoracic and lumbar spine and BMD measurements by dual x-ray absorptiometry were performed. Vertebral deformities were scored according to the method of Genant et al: fractures were defined as a reduction of > or = 20% of the vertebral body height. Osteoporosis was defined as a T score less than -2.5 SD and osteopenia as a T score less than -1.0 SD in at least 1 region of measurement. Osteopenia was present in 39% of the patients and osteoporosis in 4% (93% female; mean age 41.1 years). In multiple regression analysis, low BMD in the spine was associated with a low body mass index (BMI), postmenopausal status, and 25-hydroxyvitamin D deficiency. Low BMD in the hip was associated with low BMI and postmenopausal status. At least 1 vertebral fracture was detected in 20% of the patients. Vertebral fractures were associated with ever use of intravenous methylprednisolone and male sex. Risk factors for low BMD in SLE patients are low BMI, postmenopausal status, and vitamin D deficiency. While osteoporosis defined as a low T score was found in only 4% of the patients, osteoporotic vertebral fractures were detected in 20%. The high prevalence of low BMD and vertebral fractures implies that more attention must be paid to the prevention and treatment of osteoporosis and fractures in SLE.