1. The CYP1A1 T6235C polymorphism (rs4646903) gene polymorphism has been linked to the development of coronary heart disease and cigarette smoking-related lung cancer. The present study investigated associations between survival in acute coronary syndromes (ACS), smoking and the CYP1A1 T6235C polymorphism. 2. Patients with ACS (n = 1251) were genotyped for the CYP1A1 T6235C polymorphism. Patients had a mean age of 67.0 years, 69.8% were male and follow up occurred over a median of 1.9 years. 3. Overall genotype frequencies were CC 2.2%, TC 21.7% and TT 76.1%. The CC genotype was associated with baseline characteristics of a higher incidence of Type 2 diabetes (P = 0.017), elevated body mass index (P = 0.001) and younger age (P = 0.045). Patients with the CC genotype had significantly worse survival than TT/TC patients (P = 0.014), independent of ethnicity and established clinical risk factors. When survival was stratified by smoking history, the T6235C genotype was particularly associated with mortality in past or current smokers (mortality 23.5 vs 9.4% in CC and TT/TC patients, respectively; P = 0.019) compared with those who had never smoked (mortality 11.1 vs 11.5% in CC and TT/TC patients, respectively; P = 0.853). 4. The results indicate that the homozygous CYP1A1 6235C genotype is associated with greater mortality following the onset of ACS, independent of ethnicity and clinical risk factors, but related to smoking history.