Several factors were studied for their association with the prevalence of chronic low-back syndromes, sciatica, and unspecified low-back pain (LBP) in 2,946 women and 2,727 men (age range, 30-64 years) participating in the Mini-Finland Health Survey, a project aimed at comprehensive evaluation of the population's health. On the basis of a standardized clinical examination, a physician diagnosed sciatica in 5.1% and LBP in 11.6% of the subjects. Those with a previous traumatic back injury had a 2.5-fold risk of having sciatica or LBP. The fractions of sciatica and LBP attributable to such back injuries were estimated to be 16.5% and 13.7%, respectively. Sum indices of both physical and mental stress at work were found to be directly proportional to the prevalence of sciatica and LBP. Smokers had an increased risk of LBP, and body height was related positively to the prevalence of sciatica. These associations, however, were inconsistent between sex and age subgroups. In the presence of osteoarthritis in the knee, hip, or hand, LBP was prevalent (adjusted odds ratio [OR], 5.3; 95% confidence interval [CI], 4.1-6.9), but sciatica was not (OR, 1.1; 95% CI, 0.7-1.7). Diabetics were found to have a significantly decreased prevalence of LBP (OR, 0.4; 95% CI, 0.3-0.8). Many factors, independent of each other, determine the occurrence of chronic low-back syndromes. The determinants of sciatica and LBP are different to some extent.