Abstract Background Childhood cancer survivors exposed to abdominal radiation (abdRT) are at increased risk for diabetes mellitus, but the association between risk and radiation dose and volume is unclear. Methods Participants included 20 762 5-year survivors of childhood cancer (4568 exposed to abdRT) and 4853 siblings. For abdRT, we estimated maximum dose to abdomen; mean doses for whole pancreas, pancreatic head, body, tail; and percent pancreas volume receiving no less than 10, 20, and 30 Gy. Relative risks (RRs) were estimated with a Poisson model using generalized estimating equations, adjusted for attained age. All statistical tests were two-sided. Results Survivors exposed to abdRT (median age = 31.6 years, range = 10.2–58.3 years) were 2.92-fold more likely than siblings (95% confidence interval [CI] = 2.02 to 4.23) and 1.60-times more likely than survivors not exposed to abdRT (95%CI = 1.24 to 2.05) to develop diabetes. Among survivors treated with abdRT, greater attained age (RRper 10 years = 2.11, 95% CI = 1.70 to 2.62), higher body mass index (RRBMI 30+ = 5.00, 95% CI = 3.19 to 7.83 with referenceBMI 18.5–24.9), and increasing pancreatic tail dose were associated with increased diabetes risk in a multivariable model; an interaction was identified between younger age at cancer diagnosis and pancreatic tail dose with much higher diabetes risk associated with increasing pancreatic tail dose among those diagnosed at the youngest ages (P < .001). Radiation dose and volume to other regions of the pancreas were not statistically significantly associated with risk. Conclusions Among survivors treated with abdRT, diabetes risk was associated with higher pancreatic tail dose, especially at younger ages. Targeted interventions are needed to improve cardiometabolic health among those at highest risk.