Objectives. Larger body size is associated with larger thoracic aortic diameter, a risk factor for thoracic aortic disease (TAD). Studies of body size-indexed aortic diameters suggest wider aortas may be less harmful in large people, but the association between body size and TAD events is unknown. This study aims to assess if body size is associated with TAD events. Methods. Swedish 18-year-olds attending mandatory military conscription 1969-1997 were included. Body size was assessed as height, weight, body surface area (BSA) and body mass index (BMI) stratified into quartiles. A composite endpoint of dissection, rupture, surgery of the ascending aorta, or death from TAD was constructed, linking data from the Swedish Inpatient Register and the Cause of Death Register. Cox regression analyses, adjusted for diabetes mellitus and blood pressure at conscription, socioeconomic factors, and Marfan's syndrome, bicuspid aortic valve, and coronary artery by-pass surgery before endpoint or censoring, were performed. Results. During a median follow-up of 36 years (48,404,276 person-years), the composite endpoint occurred in 3,355 out of 1.4 million individuals, 99.7% male. The adjusted hazard ratio (95% confidence interval) for the highest versus lowest quartile of body size was 1.58 (1.43-1.73) for height, 1.90 (1.73-2.09) for weight, 1.87 (1.70-2.07) for BSA, and 1.55 (1.41-1.71) for BMI. Results were robust when surgery was excluded from the composite endpoint. Conclusions. Larger body size is associated with increased risk for TAD, regardless of the category of body size. Further studies including women, and also analyzing aortic diameter are warranted.