Context: Studies suggest that yoga is effective for moderate to severe chronic low back pain (cLBP) in diverse predominantly lower socioeconomic status populations. However, little is known about factors associated with benefit from the yoga intervention. Objective: Identify factors at baseline independently associated with greater efficacy among participants in a study of yoga for cLBP. Design: From September-December 2011, a 12-week randomized dosing trial was conducted comparing weekly vs. twice-weekly 75-minute hatha yoga classes for 95 predominantly low-income minority adults with nonspecific cLBP. Participant characteristics collected at baseline were used to determine factors beyond treatment assignment (reported in the initial study) that predicted outcome. We used bivariate testing to identify baseline characteristics associated with improvement in function and pain, and included select factors in a multivariate linear regression. Setting: Recruitment and classes occurred in an academic safety-net hospital and five affiliated community health centers in Boston, Massachusetts. Participants: Ninety-five adults with nonspecific cLBP, ages ranging from 20-64 (mean 48) years; 72 women and 23 men. Outcome measures: Primary outcomes were changes in back-related function (modified Roland-Morris Disability Questionnaire, RMDQ; 0-23) and mean low back pain intensity (0-10) in the previous week, from baseline to week 12. Results: Adjusting for group assignment, baseline RMDQ, age, and gender, foreign nationality and lower baseline SF36 physical component score (PCS) were independently associated with improvement in RMDQ. Greater than high school education level, cLBP less than 1 year, and lower baseline SF36 PCS were independently associated with improvement in pain intensity. Other demographics including race, income, gender, BMI, and use of pain medications were not associated with either outcome. Conclusions: Poor physical health at baseline is associated with greater improvement from yoga in backrelated function and pain. Race, income, and body mass index do not affect the potential for a person with low back pain to experience benefit from yoga.