Effective dose, a parameter utilized to assess biological risk related to radiation exposure, may be used to evaluate risk associated with dual-energy X-ray absorptiometry (DXA). We estimated the effective dose from DXA (Hologic QDR 4500A) scans of the lumbar spine (fast array mode), total body, hip (fast array mode), and forearm for children ages 1, 5, 10, and 15 yr and for adults. Entrance dose incorporating backscatter was determined for each scan type. Depth-dose curves were derived using Plexiglas slabs simulating tissue attenuation. Organ depth was estimated using pediatric phantom models. For all scan types, the effective dose decreased as age increased. The effective dose values for a 1-yr-old and an adult, respectively, were 4.7 microSv and 2.2 microSv for a lumbar spine scan performed in fast array mode, 3.4/3.5 microSv and 1.8/2.1 microSv (male/female) for a total body scan, and 0.14 microSv and 0.03 microSv for a forearm scan. There were marked sex differences in the effective dose associated with hip scans (fast array mode) ranging from 15.2 microSv for a 1-yr-old male to 4.6 microSv for an adult female. A comprehensive uncertainty analysis indicated that the effective dose values were reliable within a factor of 3. With the exception of the hip scans in 1- and 5-yr-olds, the effective doses were below the negligible individual dose limit of 10 microSv/yr.