The authors examined associations between back pain prevalence and lifestyle factors (smoking and obesity) using national survey data. Back pain prevalence rose with increasing levels of smoking, with a relative risk of 1.47 for persons reporting 50 or more pack-years of smoking. This association was strongest in persons under the age of 45 years, however, for whom the corresponding relative risk was 2.33. There were similar trends toward greater prevalence with increasing body mass index, but prevalence rose substantially only in the most obese 20% of subjects (1.7 times higher than the lowest 20%). In a logistic regression, smoking and obesity contributed independent risk, even after controlling for age, education, exercise level, and employment status. Programs for back pain prevention may wish to test interventions for these lifestyle-related factors.