National prevalence estimates of scoliosis in adults, based on the reading of 6594 chest X-rays from the first National Health and Nutrition Examination Survey, are presented by age, sex and race. Among US adults aged 25-74 years in 1971-75, the prevalence rate of scoliosis was 8.3%. The prevalence of scoliosis increased across age groups among women (p less than 0.001), but not among men. Women had about twice the prevalence of scoliosis as men; 10.7% versus 5.6% (p less than 0.001). Because scoliosis prevalence rates differed by age and sex, prevalence rates and means for scoliosis status subgroups were adjusted for age and sex. Blacks had a higher rate, although not statistically significant (using alpha = 0.10), of scoliosis than whites: 9.7% versus 8.1%. Bone density of the radius was lower for scoliotics than for non-scoliotics: (287.0 versus 294.0 aluminum equivalency units, p less than 0.001), suggesting a possible association between scoliosis and osteoporosis. The percentage with delayed menarche was higher for scoliotics than non-scoliotics: 37.8 versus 30.8% (p = 0.01). Scoliotic women also had a lower mean age of menstruation termination than non-scoliotic women: 43.4 years versus 44.8 years (p = 0.07). This is the first study to present national prevalence estimates for scoliosis among adults in the US.