The objectives of this study are to determine the prevalence and relative risk (RR) of back pain and identify possible mechanisms of back pain among childhood acute lymphoblastic leukemia (ALL) survivors. Surveys were mailed to 5 + -year survivors of childhood ALL aged 13 to 25 years. Survivors' siblings were also invited to participate in the study. Prevalence of back pain and hip pain among ALL survivors was determined and compared with siblings. Sex, treatment with radiation therapy, obesity, and physical activity were examined for an association with back pain and hip pain. Forty-four of 99 (44.4%) ALL survivors reported back pain compared with 11 of 52 (21.2%) their siblings (P = 0.007; RR: 2.01; 95% confidence interval = 1.15-3.56). In contrast, 10 of 99 (10.1%) ALL survivors reported experiencing hip pain compared with 1 of 52 (2.0%) siblings experiencing hip pain P = 0.07; RR: 4.95 (0.65 to 37.57). Twenty-six of 43 female survivors reported back pain compared with 18 of 56 male survivors who reported back pain (P = 0.005). Obesity, physical activity, and treatment with radiation therapy were not associated with back pain or hip pain. This is the first study demonstrating an increased frequency of back pain among survivors of childhood ALL. Future studies are needed to better define the causes of back pain among childhood ALL survivors.