Aims Our objective was to examine the association between body mass index (BMI) and survival according to the type of treatment in individuals with established coronary artery disease (CAD). Methods and results Patients with CAD were identified in the Alberta Provincial Project for Outcome Assessment in Coronary Heart Disease (APPROACH) registry between January 2001 and March 2006. Analyses were conducted separately by treatment strategy [medical management only, percutaneous coronary intervention (PCI), or coronary artery bypass grafting (CABG)]. Patients were grouped according to six BMI categories. Multivariable-adjusted hazard ratios (HRs) for mortality were calculated using the Cox regression with the referent group for all analyses being normal BMI (18.5-24.9 kg/m(2)). The cohort included 31 021 patients with a median follow-up time of 46 months. In the medically managed only group, BMIs of 25.0-29.9 and 30.0-34.9 kg/m(2) were associated with significantly lower mortality compared with normal BMI patients (adjusted HR 0.72; 95% CI 0.63-0.83 and adjusted HR 0.82; 95% CI 0.69.0-0.98, respectively). In the CABG group, BMI of 30.0-34.9 kg/m(2) had the lowest risk of mortality (adjusted HR 0.75; 95% CI 0.61-0.94), whereas in the PCI group, BMI of 35.0-39.9 kg/m(2) had the lowest risk of mortality (adjusted HR 0.65; 95% CI 0.47-0.90). Patients who were overweight or have mild or moderate obesity were also more likely to undergo revascularization procedures compared with those with normal BMI, despite having lower risk coronary anatomy. Conclusion A paradoxical association between BMI and survival exists in patients with established CAD irrespective of treatment strategy. Patients with obesity may be presenting earlier and receiving more aggressive treatment compared with those with normal BMI.