A retrospective, observational, cohort study in primary care. To determine the total direct medical and non-medical cost of chronic low back pain (LBP) in France and its associated factors. Chronic LBP affects 5-10% of the population its burden in France is unknown. Ninety-eight randomly selected general practitioners included 796 adult patients with chronic LBP between October 2001 and December 2002. Direct costs due to physician visits, investigations, medications, hospitalizations, and other medical and non-medical resource use were collected for the 6 months prior to study visit. Costs both reimbursed and not by the French health insurance system were considered. Quality of life (QoL) and disease severity were measured using Short Form (SF)-8 and Roland-Morris disability questionnaire (RMDQ), respectively. Costs were updated to represent 2007 prices. Men represented 50.6% of the 796 patients, mean age was 53 +/- 11.3 years, and the duration of LBP was more than 1 year in 80.9% of patients. The total mean cost per patient over six months was 715.6 euro (95% CI: 644.2-797.8). Of these costs, 22.9% related to care provided by physiotherapists and allied specialists, 19.5% to medications, 17.4% to hospitalizations, 9.6% to investigations, and 12.5% to physician fees. In multivariate analysis, the factors associated with the cost of chronic LBP were disease severity (RMDQ score) and age of the patients. LBP is a disease that is both common and costly.