To examine the prevalence and predictors of health insurance coverage and the difficulties obtaining coverage in a large cohort of childhood cancer survivors. This study included 12,358 5-year survivors of childhood cancer and 3,553 sibling controls participating in the Childhood Cancer Survivor Study. Data were collected by surveys distributed in 1994 (baseline) and 2000 (follow-up). At baseline, 83.9% of adult survivors, compared with 88.3% of siblings, had health insurance coverage (P < .01); 6 years later, small but significant survivor-sibling differences remained (88% v 91%; P < .01). Twenty-nine percent of survivors reported having had difficulties obtaining coverage, compared with only 3% of siblings (P < .01). In multivariate analysis of survivors 18 years of age or older, factors associated with being uninsured included younger age at diagnosis (diagnosis age of 0 to 4 years; odds ratio [OR] = 1.7; 95% CI, 1.3 to 2.2), male sex (OR = 1.3; 95% CI, 1.2 to 1.5), age at baseline survey (age 22 to 24 years; OR = 1.6; 95% CI, 1.2 to 2.1), lower level of attained education (less than high school, OR = 2.6, 95% CI, 2.1 to 3.3; high school graduate, OR = 2.1, 95% CI, 1.8 to 2.5), income less than 20,000 dollars (OR = 5.6, 95% CI, 4.5 to 7.1), marital status (widowed/divorced/separated; OR = 1.3; 95% CI, 1.1 to 1.6), smoking status (current smoker, OR = 2.0, 95% CI, 1.7 to 2.3; former smoker, OR = 1.4, 95% CI, 1.2 to 1.8), and treatment that included cranial radiation (OR = 1.3, 95% CI, 1.0 to 1.6). Compared with siblings, adult survivors of childhood cancer had significantly lower rates of health insurance coverage and more difficulties obtaining coverage. Since lack of coverage likely has serious health and financial implications for this at-risk population, any disparity in availability and quality of coverage is of great concern.