Background: General adiposity, assessed by body mass index (BMI), is a well-established cancer risk factor. This study compared waist circumference (WC), a measure of abdominal adiposity, with BMI as a risk factor for obesity-related cancers, and assessed whether WC provides additional information beyond BMI. Methods: We analyzed data from 339 190 individuals in a pooled Swedish cohort with baseline BMI and WC assessments from 1981 to 2019 (61% objectively measured, mean age 51.4 years). Cancer diagnoses were obtained from the Swedish Cancer Register. Hazard ratios (HRs) for WC and BMI were calculated using multivariable-adjusted Cox regression. To account for WC’s greater variability, we corrected HRs using regression dilution ratios. To assess WC’s additional contribution beyond BMI, we analyzed WC residuals in multivariable, BMI-adjusted models.Results: During a median follow-up of 13.9 years (interquartile range: 8.0-22.5), 18 185 IARC-established obesity-related cancers were recorded. In men, a 1-standard deviation (SD) increase in WC was associated with a 25% higher risk of obesity-related cancers (HR1-SD = 1.25, 95% CI = 1.21 to 1.30), compared to a 19% increase for BMI (HR1-SD = 1.19, 95% CI = 1.15 to 1.23, P = 0.014 for heterogeneity). Among women, associations were weaker and similar for both WC (HR1-SD = 1.13, 95% CI = 1.11 to 1.16) and BMI (HR1-SD = 1.13, 95% CI = 1.11 to 1.15, P = 0.357 for heterogeneity). Waist circumference residuals were more strongly associated with obesity-related cancer risk in men (HR1-SD = 1.09, 95% CI = 1.06 to 1.12) than in women (HR1-SD = 1.03, 95% CI = 1.02 to 1.05). Including an additional 6893 potential obesity-related cancers yielded similar patterns of associations.Conclusion(s): Waist circumference is a stronger risk factor than BMI for obesity-related cancer in men, conveying additional risk information, whereas this is less evident in women. © The Author(s) 2025.