CONTEXT: In bone mineral density (BMD) testing, unilateral hip analysis and lumbar spine measurement have been the clinical standard for diagnosis and treatment classification for postmenopausal women at risk of osteoporosis. OBJECTIVE: To determine if analysis of the bilateral hip in BMD testing has a clinical effect on diagnosis of osteoporosis and treatment classification of patients. METHODS: Dual-femur BMD test results from 313 postmenopausal women (mean age 61.2 years, range 32-90 years) were evaluated using standard BMD reference values for diagnosis and treatment classification. The author compared T scores for right and left femurs at three sites: femoral neck, trochanter, and total femur. Results: When the bilateral hip was considered in BMD testing and compared with unilateral hip results, a clinical change in diagnosis from normal to osteopenia occurred in 5.7% of subjects. In addition, a clinical change in diagnosis from osteopenia to osteoporosis occurred in 3.3% of subjects. A clinical change in treatment classification from "no treatment required" to "treatment required if one or more risk factors are present" occurred in 3% of subjects. A change in treatment classification from "treatment required if one or more risk factors are present" to "treatment required independent of risk factors" happened in 2.4% of subjects. CONCLUSION: When compared with BMD testing of the unilateral hip, inclusion of the bilateral hip in BMD testing resulted in a change in classification to a more severe diagnosis in a total of 9% of subjects, and to a more aggressive treatment category in a total of 5.4% of subjects. Dual-femur BMD testing may improve diagnosis and treatment classification for postmenopausal women at risk of osteoporosis.