The purpose of this study is to compare healthy children to children who have systemic lupus erythematosus (SLE). SLE is a childhood disease that has high risk for low bone mass and vertebral compression fractures.

The purpose of this research study is to measure bone mass in children with SLE using different measurement techniques. Children with chronic illnesses are at risk of bone fragility. This is important because bone fragility can result in childhood fractures especially children with SLE. Therefore better diagnosis technique can lead to better management of bone health.

Inclusion Criteria:

• For SLE subjects: Subjects age 5-21 drawn from rheumatology clinic at Children's Hospital of Philadelphia diagnosed with SLE for at least 1 month. Also subjects with no known vertebral compression fracture of L2.
• For Control subjects: Subjects age 5-21. Controls will be a 50% male/female.

Exclusion Criteria:

• For SLE subjects: Subjects with SLE will be excluded if they have conditions or drug exposure unrelated to SLE and known to impact growth or bone health.
• For Control subjects: Chronic disease or syndrome known to affect growth or bone health, prematurity (<37 weeks gestation), or use of any medication known to affect growth.

200 control patients (124 controls participated in unique protocol ID: 2007-10-5528 data will be used for this study, we will be trying to recruit about 76 control patients for this study) and 30 study patients with SLE