Abstract Introduction People with diabetes smoke at similar rates as those without diabetes, with cardiovascular consequences. Smoking cessation rates were compared between people with and without diabetes 1 year after an acute coronary syndrome (ACS). Aims and Methods People with ACS who smoked and were part of an observational prospective multicenter study in Switzerland were included from 2007 to 2017 and followed for 12 months. Seven-day point prevalence abstinence was assessed at 12 months follow-up. Association between diabetes and smoking cessation was assessed using multivariable-adjusted logistical regression model. Results 2457 people with ACS who smoked were included, the mean age of 57 years old, 81.9% were men and 13.3% had diabetes. At 1 year, smoking cessation was 35.1% for people with diabetes and 42.6% for people without diabetes (P-value .01). After adjustment for age, sex, and educational level, people with diabetes who smoked were less likely to quit smoking compared with people without diabetes who smoked (odds ratio [OR] 0.76, 95% confidence interval [CI] 0.59–0.98, P-value = .037). The multivariable-adjusted model, with further adjustments for personal history of previous cardiovascular disease and cardiac rehabilitation attendance, attenuated this association (OR 0.85, 95% CI 0.65–1.12, P-value = .255). Among people with diabetes, cardiac rehabilitation attendance was a positive predictor of smoking cessation, and personal history of cardiovascular disease was a negative predictor of smoking cessation. Conclusions People with diabetes who smoke are less likely to quit smoking after an ACS and need tailored secondary prevention programs. In this population, cardiac rehabilitation is associated with increased smoking cessation. Implications This study provides new information on smoking cessation following ACSs comparing people with and without diabetes. After an ACS, people with diabetes who smoked were less likely to quit smoking than people without diabetes. Our findings highlight the importance of tailoring secondary prevention to people with diabetes.