BACKGROUND: Health complications related to childhood cancer may be influenced by risky health behaviors (RHBs), particularly when RHBs co-occur. To the authors' knowledge, only limited information is available describing how RHBs cluster among survivors of childhood cancer and their siblings and the risk factors for co-occurring RHBs. METHODS: Latent class analysis was used to identify RHB clusters using longitudinal survey data regarding smoking, alcohol use, and physical activity from adult survivors (4184 survivors) and siblings (1598 siblings) in the Childhood Cancer Survivor Study. Generalized logistic regression was used to evaluate associations between demographic characteristics, treatment exposures, psychological distress, health conditions, and cluster membership. RESULTS: Three RHB clusters were identified: a low-risk cluster, an insufficiently active cluster, and a high-risk cluster (tobacco and risky alcohol use and insufficient activity). Compared with siblings, survivors were more likely to be in the insufficiently active cluster (adjusted odds ratio [ORadj ], 1.17; 95% confidence interval [95% CI], 1.06-1.27) and were less likely to be in the high-risk cluster (ORadj , 0.79; 95% CI, 0.69-0.88). Risk factors for membership in the high-risk cluster included psychological distress (ORadj , 2.76; 95% CI, 1.98-3.86), low educational attainment (ORadj , 7.49; 95% CI, 5.15-10.88), income <$20,000 (ORadj , 2.62; 95% CI, 1.93-3.57), being divorced/separated or widowed (ORadj , 1.36; 95% CI, 1.03-1.79), and limb amputation (ORadj , 1.52; 95% CI, 1.03-2.24). Risk factors for the insufficiently active cluster included chronic health conditions, psychological distress, low education or income, being obese or overweight, female sex, nonwhite race/ethnicity, single marital status, cranial radiation, and cisplatin exposure. CONCLUSIONS: RHBs co-occur in survivors of childhood cancer and their siblings. Economic and educational disadvantages and psychological distress should be considered in screening and interventions to reduce RHBs. Cancer 2016. (c) 2016 American Cancer Society. Cancer 2016;122:2747-2756. (c) 2016 American Cancer Society.