The records of 3920 patients (2068 females, 1852 males) entering a model family practice unit between 1975 and 1978 have been analyzed. Eleven percent of males and 9.5% of females reported an episode of low-back pain during that 3-year interval. The complaint of medically reported low-back pain was significantly related to occupational factors such as truck driving (P<0.001), lifting, carrying, pulling, pushing, and twisting (P<0.001 for all variables) as well as nondriving vibrational exposure (P<0.001). Patients reporting low-back pain also reported more episodes of anxiety (P<0.001) and depression (P<0.001) and had more emotionally stressful occupations (P<0.001). The mean number of pregnancies was greater in women with low-back pain (2.6) than in those without (1.6) (P<0.001). The low-back pain sufferers were more likely to be cigarette smokers (P<0.001), particularly when smoking was accompanied by a chronic cough (P<0.001). This population is currently under prospective study to define the relevance of each of these risk factors to the complaint of low-back pain.