OBJECTIVE: Type I and II diabetes are associated with a greater relative risk of cardiovascular diseases (CVD) in women than in men. Sex differences in adiposity storage may explain these findings. METHODS: A cross-sectional study of 480 813 participants from the UK Biobank without history of CVD was conducted to assess whether the difference in body size in people with and without diabetes was greater in women than in men. Age-adjusted linear regression analyses were used to obtain the mean difference in women minus men in the difference in body size measures, separately for type I and II diabetes. RESULTS: Body size was higher in individuals with diabetes than in individuals without diabetes, particularly in type II diabetes. Differences in body size between individuals with and without type II diabetes were more extreme in women than in men; compared to those without type II diabetes, body mass index and waist circumference were 1.94 (95% CI 1.82 to 2.07) and 4.84 (4.53 to 5.16) higher in women than in men, respectively. In type I diabetes, body size differed to a similar extent between those with and without diabetes in women as in men. This pattern was observed across all prespecified subgroups. CONCLUSIONS: Differences in body size associated with diabetes were significantly greater in women than in men in type II diabetes but not in type I diabetes. Prospective studies can determine whether sex differences in body size associated with diabetes underpin some of the excess risk for CVD in women with type II diabetes.