Choosing the most appropriate treatment for individual patients with low back pain (LBP) can be challenging, and clinical guidelines recommend taking into account patients' preferences. However, no tools exist to assess or compare patients' views about LBP treatments. We report the development and validation of the Low Back Pain Treatment Beliefs Questionnaire (LBP-TBQ) for use across different treatments in clinical practice and research. Using qualitative data, we developed a pool of items assessing perceived credibility, effectiveness, concerns about, and individual "fit" of specific treatments. These items were included in a survey completed by 429 primary care patients with LBP, of whom 115 completed it again 1 to 2 weeks later. We performed psychometric analyses using nonparametric item response theory and classical test theory. The 4 subscales of the resulting 16-item LBP-TBQ showed good homogeneity (H = 0.46-0.76), internal consistency (α = 0.73-0.94), and stability (r = 0.63-0.83), confirmed most convergent and discriminant validity hypotheses, and had acceptable structural validity for 4 guideline-recommended treatments: pain medication, exercise, manual therapy, and acupuncture. Participants with stronger positive treatment beliefs were more likely to rank that treatment as their first choice, indicating good criterion validity (t values = 3.11-9.80, all P < 0.01, except pain medication effectiveness beliefs, t(339) = 1.35; P = 0.18). A short 4-item version also displayed good homogeneity (H = 0.43-0.66), internal consistency (α = 0.70-0.86), and stability (r = 0.82-0.85) and was significantly related to treatment choice (t values = 4.33-9.25, all P < 0.01). The LBP-TBQ can be used to assess treatment beliefs in primary care patients with LBP and to investigate the effects of treatment beliefs on treatment uptake and adherence.