We have examined the association between body mass index and the prevalence of low back pain in about a quarter of a million male recruits aged 17-18 years at the time of their medical draft examination. Low back pain prevalence is shown to rise with increasing body mass index. This statistically significant association may suggest a role of body weight and height in the pathogenesis of low back pain and supports the previously reported need for education regarding weight reduction as a useful implement in low back pain prevention.