To identify the prevalence of chronic low back pain (CLBP) and examine factors associated with this condition in a Southern Brazilian adult population, a population-based cross-sectional study was conducted, including 3,182 subjects of both sexes, aged 20 years or over, living in the urban area of Pelotas, Rio Grande do Sul State. The questionnaire included socio-demographic, behavioral, and nutritional variables, as well as characterization of exposure to ergonomic factors in daily activities. CLBP prevalence was 4.2%. The variables sex, age, marital status, schooling, smoking, body mass index, working in a lying position, heavy physical work, and repetitive movements were associated with CLBP. Prevalence of CLBP is important as it limits normal activities and increases the use of health care services. There may be differences in the ergonomic risk factors for CLBP and low back pain in general.