Smoking is an established risk factor for aortic aneurysm, however, few studies have investigated the associations with different aortic aneurysm subsites. The aim of this study was to investigate whether different tobacco smoking metrics and smoking cessation was associated with aortic aneurysm and its subsites in the UK Biobank. The analysis included 495,993 participants, aged 37-73 years. Cox proportional hazards models were used to estimate multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between smoking and aortic aneurysm. After 12.3 years of follow-up, 3,353 incident cases and 184 deaths from aortic aneurysm were identified. The HRs (95% CIs) of aortic aneurysm incidence for current and former vs. never smokers were 4.32 (3.93-4.76) and 1.70 (1.56-1.84), respectively, and for ≥ 20 vs. <10 cigarettes per day was 5.67 (4.93-6.52), and similar results were observed for pack-years and duration of smoking. At ≥ 30 years of smoking cessation vs. current smoking risk was substantially reduced (0.23, 0.20-0.27) and comparable to never smoking (0.22, 0.20-0.25). Strong positive HRs were observed for current vs. never smoking and abdominal (8.90, 7.79-10.16), thoracoabdominal (11.64, 4.20-32.25), and unspecified site (2.06, 1.61-2.65), ruptured (10.47, 6.12-17.90) and non-ruptured (4.19, 3.80-4.62) aortic aneurysms, but no association was observed for thoracic aortic aneurysm (1.13, 0.88-1.44). Smoking was strongly associated with increased risk of aortic aneurysm and most subtypes. Smoking cessation for ≥ 30 years strongly reduced risk to levels comparable of never smokers. These findings support public health policies promoting smoking prevention and cessation.