The aim of this study was to determine if measurement of the contralateral femora has an effect on osteoporosis diagnosis and treatment classification if the spine is not included in the bone mineral density (BMD) scan. The method used was the T-score discordance from the dual femur BMD scans of 537 women (mean age: 61.2 yr; standard deviation: 10.5; age range: 32-90 yr) who were evaluated to determine if inclusion of the contralateral hip in the BMD study made a difference in clinical diagnosis and treatment classification when the spine was not included in the BMD scan. Clinical diagnosis and treatment classification was based on the lowest T-score at each hip of three femur sites: the neck, the trochanter, and the total femur. The results of the diagnosis classification (i.e., normal, osteopenia, and osteoporosis) differed in the right versus the left femora in 28% of subjects at one or more sites, and in 14%, 15%, and 10% of subjects at the neck, trochanter, and total femur, respectively. Diagnosis discordance increased in subjects who were aged 65 yr and older. Treatment classification (T>or=-1.5; T<-1.5; T<-2.0) differed in the right versus the left femora in 33% of subjects at one or more sites, and in 18%, 14%, and 12% of subjects at the neck, trochanter, and total femur, respectively. Treatment discordance increased in subjects age 65 yr and older. Using the lowest T-score for clinical diagnosis classification, when the contralateral hip was considered, a clinical difference in diagnosis from normal-->osteopenia occurred in 3.9% of subjects, and from osteopenia-->osteoporosis in 1.3% of subjects. A clinical difference in treatment category from T>or=-1.5-->T<-1.5 occurred in 2.7% of subjects, and from T>or=-2-->T<-2 in 2.7% of subjects. In conclusion, inclusion of the bilateral hip in the BMD study made a clinical difference in diagnosis classification in 5.2% of subjects and in treatment classification in 5.4% of subjects. T-score differences between the contralateral hips increased with age. In the subgroup of subjects age 65 yr and older, a clinical difference in classification to a more severe diagnosis or treatment category occurred in 5.35% and 7.25% of subjects, respectively.