Outpatient claims for the treatment of back pain in Washington State, USA, were analysed by the International Classification of Disease-9 codes and provider type. The number of visits and expenditures associated with different forms of treatments were calculated. Back pain accounted for 15% of all outpatient visits and these companies spent more than US$52 million on 652 593 claims submitted by 104 358 adults. Most people used only CAM (43%) or only conventional providers (45%) for back pain treatment, with merely 12% using both. Patients who saw only CAM providers had fewer comorbidities than the other two groups and made approximately twice as many visits as ‘conventional only’ users (median 4 vs. 2). The average amount allowed per outpatient low back pain claim was lower for CAM visits (mean US$50, SD US$28) than for conventional visits (mean US$128, SD US$173). Total out-patient costs for the treatment of back pain were highest for the group using both CAM and conventional care (mean US$1079, SD US$1185), and lowest for the group using CAM only (mean US$342, SD US$429).