Background: The relative contribution of childhood and pubertal body mass index (BMI) for the risk of adult colorectal cancer is not known. The aim of this study was to evaluate the independent associations for childhood BMI and pubertal BMI change with risk of colorectal cancer in men.Methods: We included 37,663 men born in 1946 to 1961 who had weight and height measured at 8 (childhood) and 20 (young adult age) years of age available from the BMI Epidemiology Study. Information on colorectal cancer was retrieved from the Swedish National Patient Register (257 cases of colon cancer and 159 cases of rectal cancer).Results: Childhood BMI at 8 years of age [HR, 1.19 per SD increase; 95% confidence interval (CI), 1.06-1.33], but not pubertal BMI change (HR, 1.02; 95% CI, 0.90-1.15), was associated with increased risk of colon cancer. Due to a significant interaction between childhood BMI and pubertal BMI change (P < 0.001), we stratified the analyses according to the median of pubertal BMI change. Childhood BMI was associated with risk of colon cancer in individuals with a pubertal BMI change above, but not below, the median (above: HR ¼ 1.48, 95% CI, 1.26-1.74; below: HR ¼ 0.95, 95% CI, 0.80-1.12). Neither childhood BMI nor pubertal BMI change was associated with rectal cancer.Conclusions: High childhood BMI was associated with increased risk of colon cancer only if it was followed by a pubertal BMI increase above the median.Impact: Further studies should evaluate prepubertal childhood BMI in relation to pubertal BMI change and BMI in middle age for the risk of colon cancer. NOTE: HRs for rectal cancer (n ¼ 159) according to anthropometric variables were calculated using Cox proportional hazards regression. Childhood refers to 8 years of age. Young adult BMI refers to 20 years of age. Pubertal BMI change is the change in BMI between 8 and 20 years of age. Adult height refers to the last recorded height after 17.5 years of age. The model is adjusted for birth year and country of birth. Total cohort N ¼ 37,663. Conception and design: J. C elind, C. Ohlsson, M. Bygdell, J.M. Kindblom Development of methodology: J. C elind, C. Ohlsson, M. Bygdell, J.M. Kindblom Acquisition of data (provided animals, acquired and managed patients, provided facilities, etc.): J. C elind, M. Bygdell, J.M. Kindblom Analysis and interpretation of data (e.g., statistical analysis, biostatistics, computational analysis): J. C elind, C. Ohlsson, M. Nethander, J.M. Kindblom Writing, review, and/or revision of the manuscript: J. C elind, C. Ohlsson, M. Bygdell, M. Nethander, J.M. Kindblom C elind et al.