[영문]OBJECTIVE:: We sought to compare total outpatient costs of 4 common treatments for low-back pain (LBP) at 18-months follow-up. METHODS:: Our work reports on findings from a randomized controlled trial within a large medical group practice treating HMO patients. Patients (n = 681) were assigned to 1 of 4 treatment groups, ie, medical care only (MD), medical care with physical therapy (MDPt), chiropractic care only (DC), or chiropractic care with physical modalities (DCPm). Total outpatient costs, excluding pharmaceuticals, were measured at 18 months. We did not perform a cost-effectiveness analysis because previously published findings showed no clinically meaningful difference in outcomes among the 4 treatment groups. Thirty-seven participants were lost to follow-up at 18 months, leaving a final sample size of n = 654. RESULTS:: Adjusting for covariates, DC was 51.9% more expensive than MD (P qqqlt; 0.001), DCPm 3.2% more expensive than DC (P = 0.76), and MDPt 105.8% more expensive than MD (P qqqlt; 0.001). The adjusted mean outpatient costs per treatment group were