['Prospective cohort study.', 'To describe low back pain (LBP) sustained by soldiers deployed to Afghanistan and identify demographic, fitness, and occupational risk factors of LBP.', 'LBP is the most common injury in deployed soldiers. It results in lost duty days, medical evacuations, and permanent disability. Risk factors for LBP have not been investigated in this population.', 'This study investigated a US Army Brigade Combat Team deployed to Afghanistan for 1 year. Demographic, fitness, and occupational variables were recorded before and after deployment. Episodes of LBP were assessed using self-report data. Logistic regression was used to investigate predictors of (1) moderate or worse LBP developed during deployment and (2) all LBP developed during deployment.', 'The incidence of moderate or worse LBP was 22% in the 805 soldiers studied. Soldiers with elevated risk of LBP were male, in Cavalry or Infantry units, wore body armor for more than 6 hr/d, worked at a desk for 1 to 4 hours a day, spent 5 to 8 hr/d lifting, spent more than 1 hr/wk on walking patrol, spent 21 to 40 hr/wk in a tactical vehicle, or wore equipment. The most parsimonious set of significant predictors for moderate or worse LBP included age, OR = 1.04 (1.01-1.08); fitness score, OR = 0.99 (0.989-0.999); the amount of time spent wearing body armor, OR = 1.16 (1.10-1.23); the amount of time spent on walking patrol, OR = 1.01 (1.003-1.02); and weight of the equipment worn, OR = 1.01 (1.002-1.013). The incidence of all LBP (minor or worse) was 77%. The most parsimonious set of significant predictors for all LBP included age, OR = 1.06 (1.02-1.09); fitness score, OR = 0.99 (0.985-0.997); history of LBP, OR = 2.94, (1.87-4.62); equipment weight, OR = 1.008 (1.003-1.01); and time spent wearing body armor, OR = 1.13 (1.07-1.19).'] Do loads worn by soldiers predict episodes of low back pain during deployment to Afghanistan?